The Collaborative International Dictionary of English v.0.48:

Dyscrasia \Dys*cra"si*a\, n. [NL. dyscrasia, fr. Gr. dyskrasi`a;
   dys- bad + kra^sis mixture, fr. keranny`nai to mix: cf. F.
   dycrasie.] (Med.)
   An ill habit or state of the constitution; -- formerly
   regarded as dependent on a morbid condition of the blood and
   humors.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dyscrasia
    n 1: an abnormal or physiologically unbalanced state of the body