a person or thing that reacts or undergoes reaction.
Electricity. a device whose primary purpose is to introduce reactance into a circuit.
Immunology, Veterinary Medicine. a patient or animal that reacts positively towards a foreign material.
Also called atomic pile, chain reactor, chain-reacting pile, nuclear reactor, pile. Physics. an apparatus in which a nuclear-fission chain reaction can be initiated, sustained, and controlled, for generating heat or producing useful radiation.
Chemistry. (especially in industry) a large container, as a vat, for processes in which the substances involved undergo a chemical reaction.


Origin of reactor

1885–90; 1940–45 for def 4; react + -or2
Related formsnon·re·ac·tor, noun Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for reactor

Contemporary Examples of reactor

Historical Examples of reactor

  • This will give you a constant temperature inside the reactor.

    The K-Factor

    Harry Harrison (AKA Henry Maxwell Dempsey)

  • Father, do you remember when the Haval Valley reactor blew up?

    Ministry of Disturbance

    Henry Beam Piper

  • Obviously, the reactor was the only part not vaporized in the fall—because of its construction.

    A Fine Fix

    R. C. Noll

  • Relief swept over him as he looked back at the reactor itself.

    The Bramble Bush

    Gordon Randall Garrett

  • I was finishing up with Reactor One when I heard the explosion.

    The Bramble Bush

    Gordon Randall Garrett

British Dictionary definitions for reactor



chem a substance, such as a reagent, that undergoes a reaction
short for nuclear reactor
a vessel, esp one in industrial use, in which a chemical reaction takes place
a coil of low resistance and high inductance that introduces reactance into a circuit
med a person sensitive to a particular drug or agent
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

Word Origin and History for reactor

"one that reacts," 1835, agent noun in Latin form from react. In nuclear sense, attested from 1945.

Online Etymology Dictionary, © 2010 Douglas Harper