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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," from ex- "out" (see ex-) + fundere "pour" (see found (v.2)). Figuratively, of speech, emotion, etc., from 1650s.
effusion ef·fu·sion (ĭ-fyōō'zhən)
The escape of fluid from the blood vessels or lymphatics into the tissues or a cavity.
The fluid so escaped.