si·​mul·​ta·​neous ˌsī-məl-ˈtā-nē-əs How to pronounce simultaneous (audio)
 also  ˌsi-
: existing or occurring at the same time : exactly coincident
: satisfied by the same values of the variables
simultaneous equations
 also  ˌsi-
ˌsī-məl-ˈtā-nē-əs-lē How to pronounce simultaneous (audio)
 also  ˌsi-
simultaneousness noun
Choose the Right Synonym for simultaneous

contemporary, contemporaneous, coeval, synchronous, simultaneous, coincident mean existing or occurring at the same time.

contemporary is likely to apply to people and what relates to them.

Abraham Lincoln was contemporary with Charles Darwin

contemporaneous is more often applied to events than to people.

contemporaneous accounts of the kidnapping

coeval refers usually to periods, ages, eras, eons.

two stars thought to be coeval

synchronous implies exact correspondence in time and especially in periodic intervals.

synchronous timepieces

simultaneous implies correspondence in a moment of time.

the two shots were simultaneous

coincident is applied to events and may be used in order to avoid implication of causal relationship.

the end of World War II was coincident with a great vintage year

Examples of simultaneous in a Sentence

The two gunshots were simultaneous. a simultaneous release of the movie and its soundtrack on CD
Recent Examples on the Web This area is involved with holding information in mind while doing a different simultaneous task. Sarah Raskin, Discover Magazine, 6 June 2024 Curiosity Stream supports simultaneous streaming on an unlimited number of devices. PCMAG, 4 June 2024 Hawaii's Big Island abuzz over simultaneous eruptions at Mauna Loa and Kilauea Seismic activity and ground deformation beneath the East Rift Zone and Southwest Rift Zone remain low, the agency said. Julia Jacobo, ABC News, 3 June 2024 That came just one week after thousands of autoworkers at 14 nonunion automakers launched simultaneous efforts to join the union, the UAW has said. Jamie L. Lareau, Detroit Free Press, 25 Mar. 2024 See all Example Sentences for simultaneous 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'simultaneous.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


borrowed from Medieval Latin simultāneus "occurring at the same time," from Latin simul "in company, together, at the same time" (going back to an apocopated neuter form of similis "having characteristics in common, like") + Medieval Latin -tāneus, as in instantāneus instantaneous, Late Latin momentāneus "momentary," spontāneus "voluntary, unconstrained, spontaneous" — more at similar

Note: The Dictionary of Medieval Latin from British Sources records one occurrence of simultāneus, in the Tractatus de logica of John Wycliffe. At the entry in that dictionary the word is parsed as from simultās "occurrence at the same time" (distinct from classical Latin simultās "state of animosity") + the suffix -āneus. This analysis is possible but seems less likely. Regarding the suffix -āneus see the etymology and note at spontaneous.

First Known Use

circa 1660, in the meaning defined at sense 1

Time Traveler
The first known use of simultaneous was circa 1660

Dictionary Entries Near simultaneous

Cite this Entry

“Simultaneous.” Dictionary, Merriam-Webster, Accessed 25 Jun. 2024.

Kids Definition


si·​mul·​ta·​neous ˌsī-məl-ˈtā-nē-əs How to pronounce simultaneous (audio)
: existing or occurring at the same time
: satisfied by the same values of the variables
simultaneous equations
simultaneously adverb

from Latin simul "at the same time, together" and English -taneous (as in instantaneous) — related to assemble, ensemble

More from Merriam-Webster on simultaneous

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