What word or phrase does your mother always say?
"producing the intended effect," early 15c., from Old French operatif (14c.) or directly from Late Latin operativus "creative, formative," from operat-, past participle stem of operari (see operation). Weakened sense of "significant, important" is from 1955.
"worker, operator," 1809, from operative (adj.); sense of "secret agent, spy" is first attested 1930, probably from its use by the Pinkerton Detective Agency as a title for their private detectives (1905).
operative op·er·a·tive (ŏp'ər-ə-tĭv, -ə-rā'tĭv, ŏp'rə-)
Of, relating to, or resulting from a surgical operation.
Functioning effectively; efficient.