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.
- Spreading rapidly and extensively by infection and affecting many individuals in an area or a population at the same time: an epidemic outbreak of influenza.
- Widely prevalent: epidemic discontent.
- An outbreak of a contagious disease that spreads rapidly and widely.
- A rapid spread, growth, or development: an unemployment epidemic.