op·er·ant 
(ŏpər-ənt)
(ŏpər-ənt)adj.
1. Operating to produce effects; effective.
2. Psychology Of, relating to, or being a response that occurs spontaneously and is identified by its reinforcing or inhibiting effects.
n.
1. One that operates.
2. Psychology An element of operant behavior.
[Latin operāns, operant-, present participle of operārī, to work; see OPERATE.]
oper·ant·ly adv.