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 assimilated form of ex "out" (see ex-) + fundere "to pour" (from nasalized form of PIE root *gheu- "to pour"). Figuratively, of speech, emotion, etc., from 1650s.