NOUN (1)

1. a widespread outbreak of an infectious disease; many people are infected at the same time;


ADJECTIVE (1)

1. (especially of medicine) of disease or anything resembling a disease; attacking or affecting many individuals in a community or a population simultaneously;
- Example: "an epidemic outbreak of influenza"

The Collaborative International Dictionary of English v.0.48:

Epidemic \Ep`i*dem"ic\, Epidemical \Ep`i*dem"ic*al\, a. [L.
   epidemus, Gr. ?, ?, among the people, epidemic; ? in + ?
   people: cf. F. ['e]pid['e]mique. Cf. Demagogue.]
   1. (Med.) 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.
      [1913 Webster]

   2. Spreading widely, or generally prevailing; affecting great
      numbers, as an epidemic does; as, epidemic rage; an
      epidemic evil.
      [1913 Webster]

            It was the epidemical sin of the nation. --Bp.
                                                  Burnet.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Epidemic \Ep`i*dem"ic\, n. [Cf. Epidemy.]
   1. (Med.) An epidemic disease.
      [1913 Webster]

   2. Anything which takes possession of the minds of people as
      an epidemic does of their bodies; as, an epidemic of
      terror.
      [1913 Webster]

WordNet (r) 3.0 (2006):

epidemic
    adj 1: (especially of medicine) of disease or anything
           resembling a disease; attacking or affecting many
           individuals in a community or a population
           simultaneously; "an epidemic outbreak of influenza" [ant:
           ecdemic, endemic, endemical]
    n 1: a widespread outbreak of an infectious disease; many people
         are infected at the same time