1. Occurring or completed without perceptible delay: Relief was instantaneous.
2. Done or made as quickly or directly as possible: an instantaneous reply to my letter.
3. Present or occurring at a specific instant: instantaneous velocity; instantaneous pressure.
[From Medieval Latin īnstantāneus, from Latin īnstāns, īnstant-, present; see INSTANT.]
in·stan′ta·nei·ty (ĭn-stăn′tə-nēĭ-tē, ĭn′stən-) n.
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