*acerb*

v. t. [ L. acerbatus, p. p. of acerbare, fr. acerbus. ] To sour; to imbitter; to irritate. [ 1913 Webster ]

a. Sour or severe. [ 1913 Webster ]

n. [ L. acerbitudo, fr. acerbus. ] Sourness and harshness. [ Obs. ] Bailey. [ 1913 Webster ]

n. [ F. acerbité, L. acerbitas, fr. acerbus. See Acerb. ] 1. Sourness of taste, with bitterness and astringency, like that of unripe fruit. [ 1913 Webster ]

2. Harshness, bitterness, or severity; as, acerbity of temper, of language, of pain. Barrow. [ 1913 Webster ]

v. t. [ imp. & p. p. Exacerbated p. pr. & vb. n. Exacerbating ] [ L. exacerbatus, p. p. of exacerbare; ex out (intens.) + acerbare. See Acerbate. ] To render more violent or bitter; to irritate; to exasperate; to imbitter, as passions or disease. Brougham. [ 1913 Webster ]

adj. Making worse.
Syn. -- aggravating, exasperating. [ WordNet 1.5 ]

pos>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 ]