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

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "epidemic":
   abounding, abundant, affluent, all-sufficing, ambulatory plague,
   ample, aplenty, average, besetting, black death, black plague,
   bottomless, bounteous, bountiful, bubonic plague, catching,
   cellulocutaneous plague, common, communicable, compact, contagious,
   copious, current, defervescing plague, diffuse, dominant, effuse,
   endemic, epidemial, epigrammatic, epiphytotic, epizootic,
   exhaustless, extravagant, exuberant, fat, fertile, flush, full,
   galore, general, generous, glandular plague, growth,
   hemorrhagic plague, in plenty, in quantity, inexhaustible,
   infectious, infective, inoculable, larval plague, lavish, liberal,
   luxuriant, many, maximal, meaty, much, murrain, normal, numerous,
   opulent, ordinary, outbreak, overflowing, pandemia, pandemic, pest,
   pesthole, pestiferous, pestilence, pestilential, plague,
   plague spot, plenitudinous, plenteous, plentiful, plenty,
   pneumonic plague, popular, predominant, predominating,
   premonitory plague, prevailing, prevalent, prodigal, productive,
   profuse, profusive, rampant, rash, regnant, reigning, replete,
   rich, rife, riotous, routine, ruling, running, running over,
   scourge, septicemic plague, siderating plague, sporadic, spread,
   spreading, standard, stereotyped, superabundant, taking, teeming,
   tuberculosis, universal, upsurge, usual, wealthy, well-found,
   well-furnished, well-provided, well-stocked, white plague,
   wholesale, wide-ranging, widespread, zymotic