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"that works," early 15c., from Latin operantem (nominative operans), present participle of operari "to work" (see operation). Psychological sense of "involving behavior modification" coined 1937 by U.S. psychologist B.F. Skinner (e.g. operant conditioning, 1938, Skinner).
operant op·er·ant (ŏp'ər-ənt)
Operating to produce effects; effective.
Of, relating to, or being a response that occurs spontaneously and is identified by its reinforcing or inhibiting effects.