c. 1400, "a pouring out," from Middle French effusion (14c.) and directly from Latin effusionem (nominative effusio) "a pouring forth," noun of action from past participle stem of effundere "pour forth, spread abroad; to lavish, squander, waste," from ex- "out" (see ex-) + fundere "pour" (see found (v.2)). Figuratively, of speech, emotion, etc., from 1650s.