Quick Synonym List

Closest alternatives

• at the same time
• concurrently
• at once
• together
• in parallel
• at the same moment
• at the same time as
• in tandem
• side by side
• in unison

Formal alternatives

• concurrently
• synchronously
• in parallel
• in tandem
• contemporaneously
• co-occurring
• at the same time
• at the same moment

For actions happening together

• at the same time
• concurrently
• together
• in parallel
• in tandem
• at once

For people acting together

• together
• in unison
• jointly
• collectively
• side by side
• at the same time

For technical or scientific contexts

• synchronously
• concurrently
• in parallel
• co-occurring
• coincidentally
• concurrently with

Informal alternatives

• at the same time
• at once
• together
• all at once
• at the same moment

Important: These alternatives are not identical in every context. Simultaneously emphasizes exact or overlapping timing. Concurrently often describes activities occurring during the same period. In parallel emphasizes separate processes happening alongside each other, while in unison suggests coordinated action.

What Does “Simultaneously” Mean?

Simultaneously is an adverb meaning that two or more things happen at the same time.

The two doors opened simultaneously.

Both doors opened at the same moment.

She worked and studied simultaneously.

The two activities occurred during the same period.

The system can process multiple requests simultaneously.

The requests can be handled at the same time.

The word is common in formal, academic, technical, and professional writing, but it can sometimes sound more formal than necessary in everyday conversation.

The Main Senses of “Simultaneously”

1. Simultaneously = At the Same Time

At the same time is usually the closest and most natural alternative.

The lights turned on simultaneously.

The lights turned on at the same time.

The meaning is nearly identical.

Best for

• everyday conversation
• general writing
• explanations
• emails
• informal communication

In many sentences, at the same time sounds more natural than simultaneously.

2. Simultaneously = Concurrently

Concurrently means happening or existing during the same period.

The two projects were developed simultaneously.

The two projects were developed concurrently.

This is a strong formal alternative.

Common contexts

• business
• law
• academic writing
• technology
• project management
• formal reports

Subtle difference

Simultaneously can emphasize the same moment.

Concurrently often emphasizes overlapping periods rather than exact synchronization.

For example:

The two explosions occurred simultaneously.

This strongly suggests the same moment.

The two projects ran concurrently.

This means their time periods overlapped; they do not necessarily have to start or finish at exactly the same moment.

3. Simultaneously = Together

Together can mean at the same time, especially when people or things act as a group.

They spoke simultaneously.

They spoke together.

However, the meanings are not always identical.

Simultaneously focuses on timing.

Together can focus on people acting as a group.

Compare:

The alarms sounded simultaneously.

The alarms sounded together.

The first clearly emphasizes timing. The second can sound less precise.

4. Simultaneously = At Once

At once can mean immediately or at the same time, so context matters.

The children shouted at once.

Here, it means they shouted simultaneously.

But:

Come here at once.

Here, it means immediately.

Best use

Use at once when the context clearly communicates simultaneous action. Avoid it if there is any chance the reader could interpret it as “immediately.”

5. Simultaneously = In Parallel

In parallel means that separate activities or processes occur alongside one another.

The teams worked simultaneously on different parts of the project.

The teams worked in parallel on different parts of the project.

In parallel is particularly useful in:

• business
• software development
• engineering
• project management
• research

It often emphasizes independent but overlapping processes rather than actions occurring at exactly the same instant.

6. Simultaneously = In Tandem

In tandem means two or more things operating or developing together.

The departments worked simultaneously to solve the problem.

The departments worked in tandem to solve the problem.

The second emphasizes coordination or cooperation, not simply timing.

Key distinction

Simultaneously → same time.

In tandem → together or in coordination.

They overlap but are not perfect synonyms.

7. Simultaneously = Synchronously

Synchronously means occurring at the same time or in synchronization.

It is particularly useful in technical and scientific contexts.

The devices communicate simultaneously.

The devices communicate synchronously.

Synchronously can imply that events are coordinated or synchronized according to timing.

It is more technical than ordinary simultaneously.

Common contexts

• computing
• telecommunications
• engineering
• music
• science
• data processing

8. Simultaneously = In Unison

In unison means doing or saying something together in coordinated action.

The audience clapped simultaneously.

The audience clapped in unison.

The second suggests that the clapping was coordinated and unified, not merely coincidental.

Common uses

• speak in unison
• sing in unison
• move in unison
• act in unison
• clap in unison

9. Simultaneously = At the Same Moment

At the same moment is a direct phrase-level alternative.

Both machines stopped simultaneously.

Both machines stopped at the same moment.

It strongly emphasizes a specific point in time.

Best for

• narratives
• descriptions
• explanations
• storytelling
• general writing

10. Simultaneously = Contemporaneously

Contemporaneously means occurring during the same period or at approximately the same time.

It is highly formal.

The events occurred simultaneously.

The events occurred contemporaneously.

This word is more common in legal, historical, academic, and scholarly writing.

It is not usually a good choice for casual communication.

11. Simultaneously = Jointly

Jointly means done or shared by two or more people or groups.

The organizations announced the decision simultaneously.

The organizations jointly announced the decision.

The second emphasizes shared responsibility or participation, not necessarily exact timing.

This is an important distinction.

12. Simultaneously = Collectively

Collectively means as a group or taken together.

The employees responded simultaneously.

The employees responded collectively.

These do not mean exactly the same thing.

Simultaneously = at the same time.

Collectively = as a group.

Use collectively only when the group aspect matters.

Simultaneously in Everyday English

In ordinary conversation, at the same time is usually the most natural replacement.

Example

We both arrived simultaneously.

More natural:

We both arrived at the same time.

Another example

They started talking simultaneously.

More conversational:

They started talking at the same time.

The longer phrase is not less correct. It is simply more familiar and conversational.

Simultaneously in Formal Writing

In formal writing, concurrently, simultaneously, in parallel, and contemporaneously can be useful.

Example

The two investigations were conducted simultaneously.

Possible alternatives:

The two investigations were conducted concurrently.

The two investigations were conducted in parallel.

Each emphasizes a slightly different idea.

• simultaneously → same time
• concurrently → overlapping periods
• in parallel → separate processes proceeding alongside each other

Simultaneously in Academic Writing

Academic writing often uses simultaneously when describing multiple effects or processes.

The intervention increased productivity while simultaneously reducing costs.

This is natural because both outcomes occurred together.

Possible rewrite:

The intervention increased productivity while at the same time reducing costs.

This is slightly less formal but often easier to read.

Another example

The study examined two variables simultaneously.

→

The study examined two variables at the same time.

Both are correct.

Simultaneously is more concise and formal.

Simultaneously in Business Writing

Useful alternatives include:

• concurrently
• in parallel
• in tandem
• at the same time
• jointly

Example

We launched the two campaigns simultaneously.

Depending on the intended meaning:

We launched the two campaigns concurrently.

We developed the campaigns in parallel.

The two teams worked in tandem.

These are not interchangeable in every case.

Simultaneously in Technical Writing

Technical contexts may distinguish between simultaneous, concurrent, parallel, and synchronous processes.

Simultaneous

Events happen at the same time.

Concurrent

Processes overlap in time, but they do not necessarily occur at exactly the same instant.

Parallel

Processes operate alongside each other, often independently.

Synchronous

Processes or events are coordinated according to timing.

These distinctions can matter in computing, engineering, telecommunications, and scientific writing.

Simultaneously vs. At the Same Time

These are usually the closest alternatives.

Important extra meaning

At the same time can also mean however or nevertheless.

The job is difficult. At the same time, it is rewarding.

You cannot replace this use with simultaneously.

❌ The job is difficult. Simultaneously, it is rewarding.

The meaning changes.

Simultaneously vs. Concurrently

These are close but not identical.

Simultaneously generally suggests events occurring at the same time.

Concurrently often means happening during overlapping periods.

The two shots were fired simultaneously.

This strongly suggests the same moment.

The two projects were conducted concurrently.

This suggests that they were active during the same period.

Simultaneously vs. Together

Together can describe simultaneous action but often adds the idea of unity or cooperation.

They raised their hands simultaneously.

They raised their hands together.

The first focuses on timing.

The second can suggest coordinated group action.

Simultaneously vs. In Parallel

In parallel emphasizes multiple processes occurring alongside each other.

The teams worked simultaneously.

The teams worked in parallel.

The second suggests that the teams were working on separate but related tasks.

It is especially common in technical and professional contexts.

Simultaneously vs. In Tandem

In tandem means together or in coordination.

The two systems operated simultaneously.

The two systems operated in tandem.

The second may suggest that the systems worked together, not merely that they operated at the same time.

Simultaneously vs. Synchronously

Synchronously suggests coordination or synchronization.

The signals were transmitted simultaneously.

The signals were transmitted synchronously.

The second is more technical and may imply that the signals were intentionally coordinated in time.

Simultaneously vs. At Once

These can overlap, but at once has two meanings.

Everyone answered at once.

= Everyone answered simultaneously.

But:

Leave at once.

= Leave immediately.

Because of this ambiguity, at the same time is often clearer when you mean simultaneous action.

Comparison Table

Stronger and More Precise Alternatives

Instead of looking for a more sophisticated synonym, choose a phrase that communicates the exact relationship between events.

Sentence Transformations

1. Everyday English

Original:

The two children spoke simultaneously.

Better Alternative:

The two children spoke at the same time.

Why: At the same time is more natural in everyday conversation.

2. Formal writing

Original:

The projects were developed simultaneously.

Better Alternative:

The projects were developed concurrently.

Why: Concurrently is a useful formal alternative when the projects overlap in time.

3. Technical context

Original:

The systems process the requests simultaneously.

Better Alternative:

The systems process the requests in parallel.

Why: In parallel emphasizes separate processes operating alongside one another.

4. Coordinated action

Original:

The performers moved simultaneously.

Better Alternative:

The performers moved in unison.

Why: In unison adds the idea of coordinated movement.

5. Cooperation

Original:

The departments worked simultaneously to solve the problem.

Better Alternative:

The departments worked in tandem to solve the problem.

Why: In tandem emphasizes cooperation rather than merely shared timing.

6. Exact timing

Original:

The alarms went off simultaneously.

Better Alternative:

The alarms went off at the same moment.

Why: At the same moment clearly emphasizes exact timing.

7. Academic writing

Original:

The treatment reduced pain while simultaneously improving mobility.

Better Alternative:

The treatment reduced pain while at the same time improving mobility.

Why: The phrase is slightly less formal while preserving the meaning.

8. Formal historical writing

Original:

Several events occurred simultaneously.

Better Alternative:

Several events occurred contemporaneously.

Why: Contemporaneously is highly formal and can fit scholarly or historical contexts.

9. Shared responsibility

Original:

The companies announced the partnership simultaneously.

Better Alternative:

The companies jointly announced the partnership.

Why: Jointly emphasizes that the announcement was made by the companies together, not necessarily that the announcements occurred at precisely the same instant.

10. Casual emphasis

Original:

Everyone started laughing simultaneously.

Better Alternative:

Everyone started laughing all at once.

Why: All at once sounds more conversational and expressive.

Common Collocations With “Simultaneously”

Useful combinations include:

• occur simultaneously
• happen simultaneously
• operate simultaneously
• work simultaneously
• act simultaneously
• appear simultaneously
• launch simultaneously
• develop simultaneously
• operate simultaneously
• process simultaneously
• run simultaneously
• respond simultaneously
• speak simultaneously
• arrive simultaneously
• occur simultaneously with
• simultaneously increase
• simultaneously reduce
• simultaneously improve

Common sentence structure

while simultaneously + verb-ing

For example:

The company reduced costs while simultaneously improving service.

This structure is common in professional and academic writing.

Grammar and Usage

Simultaneously is an adverb.

It commonly modifies a verb:

The machines operated simultaneously.

It can also appear before a main verb:

The system simultaneously processes several requests.

Or after an auxiliary/modal verb:

The software can simultaneously handle multiple tasks.

“Simultaneously with”

Use simultaneously with when directly connecting two events or activities.

The announcement was made simultaneously with the product launch.

You can also use:

simultaneously while

But avoid unnecessary combinations when a simpler construction works.

Common Mistakes

1. Using “simultaneously” when you mean “immediately”

At once can mean either “simultaneously” or “immediately,” but simultaneously only refers to timing.

Everyone spoke at once.

= Everyone spoke simultaneously.

Leave at once.

= Leave immediately.

2. Treating “concurrently” as perfectly identical

Concurrently often means that activities overlap in time. They do not necessarily begin or end at the same moment.

3. Using “in tandem” simply to mean “at the same time”

In tandem emphasizes cooperation or coordination.

4. Using “in unison” for unrelated events

In unison usually implies coordinated group action.

5. Confusing “simultaneously” with “jointly”

Jointly emphasizes shared participation or responsibility, not timing.

6. Overusing technical terms

Words such as synchronously and contemporaneously can make ordinary writing unnecessarily formal.

The two teams met synchronously.

Usually:

The two teams met at the same time.

is clearer.

7. Forgetting the second meaning of “at the same time”

At the same time can mean however or nevertheless.

I understand your point. At the same time, I disagree.

This is not a simultaneous-action meaning.

When Not to Replace “Simultaneously”

Keep simultaneously when you want a concise, precise adverb and the sentence is already clear.

The two events occurred simultaneously.

The software can perform several tasks simultaneously.

She was simultaneously excited and nervous.

In the last example, at the same time is possible:

She was excited and nervous at the same time.

But simultaneously gives the sentence a more compact and formal style.

Do not replace the word merely because you want to avoid repetition. If simultaneously is the clearest option, it is often better to keep it.