[ ree-ak-tiv-i-tee ]
/ ˌri ækˈtɪv ɪ ti /


the quality or condition of being reactive.
Chemistry. the relative capacity of an atom, molecule, or radical to undergo a chemical reaction with another atom, molecule, or compound.
Physics. a measure of the deviation from the condition at which a nuclear reactor is critical.
Immunology. the ability of an antigen to combine with an antibody.

Nearby words

  1. reactive depression,
  2. reactive hyperemia,
  3. reactive schizophrenia,
  4. reactive thrust,
  5. reactively,
  6. reactor,
  7. reactor vessel,
  8. reactor, nuclear,
  9. read,
  10. read a lecture

Origin of reactivity

First recorded in 1885–90; reactive + -ity

Related formshy·per·re·ac·tiv·i·ty, noun Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Medicine definitions for hyperreactivity


[ rē′ăk-tĭvĭ-tē ]


The property of reacting.
The process of reacting.

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