reactor

UK: /riˈæktə^r/ US: /riˈæktɚ/ ,(rē ak′tər)

WordReference Random House Learner's Dictionary of American English © 2026

re•ac•tor /riˈæktɚ/   n. 

[countable]
1. one that reacts.
2. Energy, Physics an apparatus in which a nuclear-fission chain reaction is sustained and controlled.

WordReference Random House Unabridged Dictionary of American English © 2026

re•ac•tor  (rē ak′tər), n. 

1. a person or thing that reacts or undergoes reaction.
2. [Elect.] a device whose primary purpose is to introduce reactance into a circuit.
3. Immunology, Veterinary Diseases a patient or animal that reacts positively towards a foreign material.
4. Energy, Physics 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.
5. Chemistry (esp. in industry) a large container, as a vat, for processes in which the substances involved undergo a chemical reaction.

• 1885–90; 1940–45 for def. 4; react + -or²

Collins Concise English Dictionary © HarperCollins Publishers::

reactor / rɪˈæktə/ noun

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