1. (Science: epidemiology) Common to, or affecting at the same time, a large number in a community; applied to a disease which, spreading widely, attacks many persons at the same time; as, an epidemic disease; an epidemic catarrh, fever, etc. See endemic.
2. Spreading widely, or generally prevailing; affecting great numbers, as an epidemic does; as, epidemic rage; an epidemic evil. It was the epidemical sin of the nation. (bp. Burnet)
Origin: L. Epidemus, gr, among the people, epidemic; in _ people: cf. F. Epidemique. Cf. Demagogue.