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[ree-ak-tiv] /riˈæk tɪv/
tending to react.
pertaining to or characterized by reaction.
Electricity. pertaining to or characterized by reactance.
Origin of reactive
First recorded in 1705-15; react + -ive
Related forms
reactively, adverb
reactiveness, noun
antireactive, adjective
hyperreactive, adjective
nonreactive, adjective
overreactive, adjective
unreactive, adjective
Can be confused
proactive, reactionary, reactive. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for reactive
Contemporary Examples
Historical Examples
  • They rise and fall together; they are reactive, one upon the other.

  • Succedaneum for Chrysarobin; very active reducer or "reactive."

    Merck's 1899 Manual Merck & Co.
  • The bandolero was languishing in the third reactive stage of malignant cholera.

    The Wolf Cub Patrick Casey
  • But they had been replaced by an uncontrollable, reactive nausea.

    Spillthrough Daniel F. Galouye
  • But there are many possible tracer rays not reactive to a screen such as I was using.

    Skylark Three Edward Elmer Smith
British Dictionary definitions for reactive


readily partaking in chemical reactions: sodium is a reactive metal, free radicals are very reactive
of, concerned with, or having a reactance
responsive to stimulus
(of mental illnesses) precipitated by an external cause: reactive depression
Derived Forms
reactively, adverb
reactivity (ˌriːækˈtɪvɪtɪ), reactiveness, noun
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 reactive

1712, from react + -ive. Related: Reactively; reactiveness; reactivity.

Online Etymology Dictionary, © 2010 Douglas Harper
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reactive in Medicine

reactive re·ac·tive (rē-āk'tĭv)

  1. Tending to be responsive or to react to a stimulus.

  2. Characterized by reaction.

  3. Tending to participate readily in chemical reactions.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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