The Collaborative International Dictionary of English v.0.48:

Epizootic \Ep`i*zo*["o]t"ic\, Epizooty \Ep`i*zo"["o]*ty\, n. [F.
   ['e]pizo["o]tie.]
   1. A contagious disease which attacks many animals at the
      same time; an epizootic disease; an epidemic among
      animals.
      [1913 Webster]

   2. A murrain; an epidemic influenza among horses.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Epizootic \Ep`i*zo*["o]t"ic\, a. [Cf. F. ['e]pizo["o]tique.]
   1. (Zo["o]l.) Of or pertaining to an epizo["o]n.
      [1913 Webster]

   2. (Geol.) Containing fossil remains; -- said of rocks,
      formations, mountains, and the like. [Obs.]
      [1913 Webster]

            Epizo["o]tic mountains are of secondary formation.
                                                  --Kirwan.
      [1913 Webster]

   3. Of the nature of a disease which attacks many animals at
      the same time; -- corresponding to epidemic diseases among
      men.
      [1913 Webster] Epizooty

WordNet (r) 3.0 (2006):

epizootic
    adj 1: (of animals) epidemic among animals of a single kind
           within a particular region; "an epizootic disease"