The Collaborative International Dictionary of English v.0.48:

Acerbity \A*cerb"i*ty\, n. [F. acerbit['e], 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]

WordNet (r) 3.0 (2006):

acerbity
    n 1: a sharp bitterness
    2: a sharp sour taste [syn: acerbity, tartness]
    3: a rough and bitter manner [syn: bitterness, acrimony,
       acerbity, jaundice, tartness, thorniness]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "acerbity":
   acescency, acid, acidity, acidness, acidulousness, acridity,
   acridness, acrimony, animosity, asperity, astringence, astringency,
   bile, bite, bitingness, bitter pill, bitter resentment, bitterness,
   bitterness of spirit, causticity, causticness, choler,
   corrosiveness, crabbedness, cuttingness, dourness, dryness, edge,
   fierceness, gall, gall and wormwood, gnashing of teeth, greenness,
   grip, hard feelings, harshness, heartburning, hyperacidity,
   incisiveness, keenness, mordacity, mordancy, piercingness,
   piquancy, poignancy, point, pungency, rancor, rankling, rigor,
   roughness, severity, sharpness, slow burn, soreness, sour,
   sourishness, sourness, spleen, stabbingness, sting, stridency,
   stringency, subacidity, surliness, tartishness, tartness, teeth,
   trenchancy, unripeness, unsweetness, vehemence, verjuice,
   vinegariness, vinegarishness, violence, virulence