reactor

American  

[ree-ak-ter] / riˈæk tər /

noun

1. a person or thing that reacts or undergoes reaction.

2. Electricity. a device whose primary purpose is to introduce reactance into a circuit.

3. Immunology, Veterinary Medicine. a patient or animal that reacts positively towards a foreign material.

4. Physics. nuclear reactor.

5. Chemistry. (especially in industry) a large container, as a vat, for processes in which the substances involved undergo a chemical reaction.

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reactor British  

/ rɪˈæktə /

noun

1. chem 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. med a person sensitive to a particular drug or agent

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Other Word Forms

• nonreactor noun

Etymology

Origin of reactor

First recorded in 1885–90; 1940–45 reactor for def. 4; react + -or ²

Explanation

A reactor is where a nuclear reaction is controlled, making it possible to create energy or any number of artificial elements. Reactor these days almost always refers to a nuclear reactor, where atomic fission of uranium or plutonium creates the heat used to make steam to generate electricity. Originally, though, reactor meant a vessel in which chemical processes were made to generate useful products such as nylon and artificial sweetener. These reactors are still used in chemical manufacturing plants.

Example Sentences

She sat alongside a nuclear reactor during a flight with Energy Secretary Chris Wright; she still isn’t quite sure she understands what a nuclear reactor is.

From The Wall Street Journal • Apr. 11, 2026

Tehran then turned to Russia, which took over the contract in January 1995, aiming to commission the 1,000-megawatt pressurized water reactor in 1999.

From Barron's • Apr. 4, 2026

Not everyone is fully on board, however — including Isaacman, whose ambitious plans involve developing a lunar nuclear reactor by 2030.

From MarketWatch • Mar. 31, 2026

Dan Eggers, Constellation’s senior vice president for finance, told Barron’s last week that any new reactor investments would have to clear a high bar.

From Barron's • Mar. 30, 2026

At about the same time as the explosion in unit 4, operators in the unit 2 control room had thought they heard another explosion coming from the torus beneath reactor 2.

From "Meltdown" by Deirdre Langeland