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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. 2018.
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Examples from the Web for simultaneity
Historical Examples
  • Twins they were in simultaneity of birth, but not in likeness of growth.

  • We have not a direct intuition of simultaneity, nor of the equality of two durations.

    Major Prophets of To-Day Edwin E. Slosson
  • This simultaneity and concurrency are central tenets of imposing Shock and Awe.

    Shock and Awe Harlan K. Ullman
  • One may not appear twice in simultaneity upon the Time-scroll.

  • He was interested by the celerity, the simultaneity of his impressions, his reflections.

    Literature and Life William Dean Howells
  • The unity of this general present fact is expressed by the concept of simultaneity.

    The Concept of Nature Alfred North Whitehead
  • Harmony is simultaneity and a painting in this respect is a chord—a momentary expression fixed in material media.

    Artificial Light M. Luckiesh
  • And, as far as the laws of simultaneity would allow, it was midnight in Greenwich, England.

    Unwise Child Gordon Randall Garrett
  • Priority and simultaneity, in this direct and primary sense, are among the clearest and most impressive notions of the human mind.

    Aristotle George Grote
  • We build on the trends of rapidity and simultaneity and seek to emphasize control and time.

    Shock and Awe Harlan K. Ullman
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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