simultaneous

American  

[sahy-muhl-tey-nee-uhs, sim-uhl-] / ˌsaɪ məlˈteɪ ni əs, ˌsɪm əl- /

adjective

1. existing, occurring, or operating at the same time; concurrent: simultaneous translation.

   simultaneous movements;

   simultaneous translation.

   Synonyms:

   coincident, synchronous

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simultaneous British  

/ ˌsaɪməltəˈniːɪtɪ, ˌsɪməltəˈniːɪtɪ, ˌsaɪməlˈteɪnɪəs, ˌsɪməlˈteɪnɪəs /

adjective

1. occurring, existing, or operating at the same time; concurrent

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noun

1. Sometimes shortened to: simul.  chess a display in which one player plays a number of opponents at once, walking from board to board

Other Word Forms

• nonsimultaneous adjective
• simultaneity noun
• simultaneously adverb
• simultaneousness noun
• unsimultaneous adjective
• unsimultaneousness noun

Etymology

Origin of simultaneous

First recorded in 1650–60; from Latin simul “together” ( similar ) + (instan)taneous

Explanation

The adjective simultaneous describes something that is done at the same time as something else. "The teachers all assigned simultaneous projects to the students that week. The kids were grumbling and sleep-deprived due to the grind." The Latin root of simultaneous is simul, which also means "at the same time." One way to remember this word is to think of simulcast programs that are simultaneously available through different television networks, radio stations or Web sites — so you can catch that concert on TV while your friend is listening to it on his car radio.

Example Sentences

The protest erupted after federal agents conducted simultaneous immigration raids at the company’s Camarillo and Carpinteria locations, arresting more than 300 workers without documentation.

From Los Angeles Times • Apr. 10, 2026

"We demonstrated that this synergistic effect is not a coincidence, but is based on a novel mode of action resulting from the simultaneous activation of different intracellular signaling pathways," says Prof. Arimura.

From Science Daily • Apr. 9, 2026

Look more closely at many major innovations throughout history and you’ll find a similar process of so-called simultaneous invention—different researchers consuming the same material and reaching similar conclusions independently.

From The Wall Street Journal • Apr. 5, 2026

Put spreads involve the simultaneous purchase and sale of put options with the same expiry but different strike prices.

From MarketWatch • Apr. 1, 2026

But all of these terms refer to two or more independent, simultaneous melodies.

From "Understanding Basic Music Theory" by Catherine Schmidt-Jones and Russel Jones

Related Words

• concurrent