The Collaborative International Dictionary of English v.0.48:

Zymotic \Zy*mot"ic\, a. [Gr. ? causing to ferment, fr. ? to
   ferment, ? ferment, leaven.]
   [1913 Webster]
   1. Of, pertaining to, or caused by, fermentation.
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   2. (Med.) Designating, or pertaining to, a certain class of
      diseases. See Zymotic disease, below.
      [1913 Webster]

   Zymotic disease (Med.), any epidemic, endemic, contagious,
      or sporadic affection which is produced by some morbific
      principle or organism acting on the system like a ferment.
      [1913 Webster]