simultaneous

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

Synonyms of simultaneous

• 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

The two gunshots were simultaneous.

a simultaneous release of the movie and its soundtrack on CD

Recent Examples on the Web

This simultaneous, contrasting discourse highlights a deep bifurcation in the AI industry regarding safety, regulation, and the future trajectory of superintelligence, with competitive interests underlying the philosophical debate. — Anisha Sircar, Forbes.com, 30 July 2026

As per usual, the Artios Awards will be presented during simultaneous ceremonies at The Beverly Hilton in Beverly Hills, the Edison Ballroom in New York City and One Moorgate Place in London. — Erik Pedersen, Deadline, 27 July 2026

Less noticed, but fundamentally important, is a simultaneous number of government announcements of new regulatory actions. — Robert Greifeld, CNBC, 27 July 2026

The subscription covers unlimited simultaneous device connections, so one account works across phones, laptops, tablets, and smart TVs without restriction. — Stackcommerce Team, PC Magazine, 24 July 2026

Word History

Etymology

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

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

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