The Collaborative International Dictionary of English v.0.48:

Exacerbation \Ex*ac`er*ba"tion\
   ([e^]gz*[a^]s`[~e]r*b[=a]"sh[u^]n) n. [Cf. F. exacerbation.]
   1. The act of rendering more violent or bitter; the state of
      being exacerbated or intensified in violence or malignity;
      as, exacerbation of passion.
      [1913 Webster]

   2. (Med.) A periodical increase of violence in a disease, as
      in remittent or continuous fever; an increased energy of
      diseased and painful action.
      [1913 Webster]

WordNet (r) 3.0 (2006):

exacerbation
    n 1: action that makes a problem or a disease (or its symptoms)
         worse; "the aggravation of her condition resulted from lack
         of care" [syn: aggravation, exacerbation]
    2: violent and bitter exasperation; "his foolishness was
       followed by an exacerbation of their quarrel"