c.1600, "common to or affecting a whole people," originally and usually, though not etymologically, in reference to diseases, from French épidémique, from épidemié "an epidemic disease," from Medieval Latin epidemia, from Greek epidemia "a stay in a place; prevalence of an epidemic disease" (especially the plague), from epi "among, upon" (see epi-) + demos "people, district" (see demotic).

1757, "an epidemic disease, a temporary prevalence of a disease throughout a community," from epidemic, adj.; earlier epideme (see epidemy). An Old English noun for this (persisting in Middle English) was man-cwealm.