operant

Etymology

adj

1. That operates to produce an effect.
   thy most operant poison
   I tell you frankly, if Paul Aubry is guilty I hope is convicted and punished; but if one of the others is guilty I hope he—or she—is punished, and if I knew anything operant to that end I certainly would not withhold it. 1955, Rex Stout, "When a Man Murders...", in Three Witnesses, October 1994 Bantam edition, page 117

noun

1. An operative person or thing.
2. (psychology) Any of a class of behaviors that produce consequences by operating (i.e., acting) upon the environment.