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

adjective

catalytic

noun

activator , catalyst