Etymology From Middle English operant, from Latin operāns.
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