operative (adj.)

late 15c., operatif, "active, working," from Old French operatif (14c.) and directly from Medieval Latin operativus "creative, formative," from operat-, past-participle stem of operari (see operation). Meaning "producing the intended effect" is from 1590s.

1809, "worker, operator, artisan," from operative (adj.); sense of "secret agent, spy" is attested from 1930, probably from its use by the Pinkerton Detective Agency as a title for their private detectives (1905) to avoid the term detective.