Pronunciation: (rē-ak'tur),[key] —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. Immunol.,Vet. Med.a patient or animal that reacts positively towards a foreign material.
4. 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. Chem.(esp. in industry) a large container, as a vat, for processes in which the substances involved undergo a chemical reaction.