Definition of: reactor

(rē·ak′tər) noun
1. One who or that which reacts.
2. Electr. A device for introducing reactance into a circuit, as for starting motors, controlling current, and the like.
3. Biol. An animal or person giving a positive reaction to a specified bacteriological or medical test.
4. Physics Any of variously designed assemblies for the initiation and control of nuclear fission, consisting essentially of reserves of fissionable material used as fuel, moderators to check the rate of nuclear reactions, reflectors, and auxiliary structures, equipment, shielding, etc.: also called pile.