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"

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "exacerbation":
   accelerando, acceleration, aggravation, agitation, amplification,
   animation, annoyance, arousal, arousing, augmentation, beefing-up,
   blowing up, blowup, chafe, concentration, condensation,
   consolidation, contentiousness, deepening, deliberate aggravation,
   deterioration, electrification, embittering, embitterment,
   enhancement, enlargement, exaggeration, exasperation, excitation,
   excitement, exhilaration, explosion, fomentation, fret, gall,
   galvanization, heating-up, heightening, incitement, increase,
   inflammation, information explosion, infuriation, intensification,
   irritant, irritation, lathering up, magnification, perturbation,
   pickup, population explosion, provocation, redoubling,
   reinforcement, sharpening, souring, speedup, steaming up, step-up,
   stimulation, stimulus, stirring, stirring up, strengthening,
   tightening, whipping up, working up, worsening