simultaneous

1 of 2

adjective

si·​mul·​ta·​neous ˌsī-məl-ˈtā-nē-əs 

-nyəs

also ˌsi-

1

: existing or occurring at the same time : exactly coincident

2

: satisfied by the same values of the variables

simultaneous equations

simultaneity

ˌsī-məl-tə-ˈnē-ə-tē  -ˈnā- 

also ˌsi-

noun

simultaneously

ˌsī-məl-ˈtā-nē-əs-lē 

-nyəs-

also ˌsi-

adverb

simultaneousness noun

simultaneity

2 of 2

noun

simul·​ta·​ne·​i·​ty

ˌsīməltəˈnēətē, 

ˌsim-, 

-ēətē, 

-i

plural -es

: the quality or state or an instance of being simultaneous

the simultaneity of these events has been exaggerated

—G. G. Simpson

specifically : the presentation of different views of the same object (such as a profile and full view of a face) in one work of art

simultaneity … in Egyptian painting

—Helen Gardner

Synonyms of simultaneous

Adjective

• concurrent
• synchronous
• synchronic
• coincident

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

Adjective

The two gunshots were simultaneous.

a simultaneous release of the movie and its soundtrack on CD

Recent Examples on the Web

Adjective

And this current El Niño is especially a wildcard given the simultaneous influence of global warming due to climate pollution, which could worsen some of El Niño’s impacts. — Andrew Freedman, CNN Money, 25 Aug. 2026

The existing physical experiments and standard computational models cannot isolate these simultaneous microscale behaviors. — Mrigakshi Dixit, Interesting Engineering, 24 Aug. 2026

Kicking your tier up to Unlimited gives you 10 simultaneous high-speed connections and access to all servers. — Neil J. Rubenking, PC Magazine, 24 Aug. 2026

The Bell Jar Tracing the tangle of a new job in New York City and the simultaneous onrush of clinical depression, The Bell Jar brings the interior world of central character Esther Greenwood into stunning relief. — Caroline Rogers, Southern Living, 22 Aug. 2026

Word History

Etymology

Adjective

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.

Noun

Medieval Latin simultaneitas, from (assumed) Medieval Latin simultaneus + Latin -itas -ity

First Known Use

Adjective

circa 1660, in the meaning defined at sense 1

Rhymes for simultaneous

• miscellaneous
• percutaneous
• subcutaneous
• subterraneous
• transcutaneous
• contemporaneous
• extemporaneous
• intracutaneous
• mucocutaneous
• extraneous
• spontaneous
• lanius

Kids Definition

simultaneous

adjective

si·​mul·​ta·​neous ˌsī-məl-ˈtā-nē-əs 

-nyəs

1

: existing or occurring at the same time

2

: satisfied by the same values of the variables

simultaneous equations

simultaneously adverb

Etymology

Adjective

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