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[sahy-muh l-tey-nee-uh s, sim-uh l-] /ˌsaɪ məlˈteɪ ni əs, ˌsɪm əl-/
existing, occurring, or operating at the same time; concurrent:
simultaneous movements; simultaneous translation.
Origin of simultaneous
1650-60; < Latin simul together (see similar) + (instan)taneous
Related forms
simultaneously, adverb
simultaneousness, simultaneity
[sahy-muh l-tuh-nee-i-tee, sim-uh l-] /ˌsaɪ məl təˈni ɪ ti, ˌsɪm əl-/ (Show IPA),
nonsimultaneous, adjective
nonsimultaneously, adverb
unsimultaneous, adjective
unsimultaneously, adverb
unsimultaneousness, noun
synchronous, coincident. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for simultaneity
  • Also, the hypothesis of simultaneity is tested to determine if the two decisions are actually endogenous to each other.
  • They slosh out into a bog, and with inexplicable simultaneity, begin applauding wildly.
  • The sinister violence of the deaths, their astounding suddenness and gruesomeness and simultaneity, stamped them as horrific.
  • People found out about the tragedy in near simultaneity, and together watched the story evolve on television.
  • Thus he concluded that the simultaneity on the ground is not on the train.
  • Scientists are now beginning to solve the mystery of this feat of simultaneity.
  • Since the two photons are traveling in the same reference frame, all of their events share simultaneity.
  • What they value is not worker stability but constant market simultaneity.
  • But the point is, relativity has rendered obsolete the concept of simultaneity.
  • Of course the key to this is relativity of simultaneity.
British Dictionary definitions for simultaneity


/ˌsɪməlˈteɪnɪəs; US ˌsaɪməlˈteɪnɪəs/
occurring, existing, or operating at the same time; concurrent
(chess) a display in which one player plays a number of opponents at once, walking from board to board Sometimes shortened to simul
Derived Forms
simultaneously, adverb
simultaneousness, simultaneity (ˌsɪməltəˈniːɪtɪ; US) (ˌsaɪməltəˈniːɪtɪ) noun
Word Origin
C17: formed on the model of instantaneous from Latin simul at the same time, together
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for simultaneity

1650s, from simultaneous + -ity.



1650s, from Medieval Latin simultaneus, perhaps from simultim "at the same time," extended from Latin simul "at the same time" (see similar (adj.)), or from simul with ending abstracted from Late Latin spontaneus, where the -t- is organic. Related: Simultaneously.

Online Etymology Dictionary, © 2010 Douglas Harper
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