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]