Meaning of REACTOR in English

■ noun

1》 (also nuclear ~ ) an apparatus or structure in which fissile material can be made to undergo a controlled, self-sustaining nuclear reaction with the consequent release of energy.

2》 a container or apparatus in which substances are made to react chemically.

3》 Medicine a person who reacts to a drug, antigen, etc.

4》 Physics a coil or other component which provides reactance in a circuit.

Concise Oxford English vocab.      Сжатый оксфордский словарь английского языка.