Source : Webster's Revised Unabridged Dictionary (1913)

Operant \Op"er*ant\, a. [L. operans, p. pr. of operari. See
   {Operate}.]
   Operative. [R.] --Shak. -- n. An operative person or thing.
   [R.] --Coleridge.

Source : WordNet®

operant
     adj : having influence or producing an effect; "many emotional
           determinants at work"; "an operant conscience" [syn: {at
           work(p)}]