adj. 1. Happening, existing, or done at the same time. See Synonyms at contemporary. 2. Mathematics Containing variables for which there are values that can satisfy all the equations: simultaneous equations. [Latin simul, at the same time; see sem-1 in the Appendix of Indo-European roots + English -taneous (as in INSTANTANEOUS).] si′mul·tane·ous·ly adv. si′mul·tane·ous·ness, si′mul·ta·nei·ty (-tə-nēĭ-tē, -nā-) n. |
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