early 13c., "an emotion of the mind, passion, lust as opposed to reason," from Old French afection (12c.) "emotion, inclination, disposition; love, attraction, enthusiasm," from Latin affectionem (nominative affectio) "a relation, disposition; a temporary state; a frame, constitution," noun of state from past participle stem of afficere "to do something to, act on" (see affect, n.). Sense developed from "disposition" to "good disposition toward" (late 14c.). Related: Affections.