The Collaborative International Dictionary of English v.0.48:

Acerbic \A*cerb"ic\, a.
   Sour or severe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acerbic
    adj 1: sour or bitter in taste [syn: acerb, acerbic,
           astringent]
    2: harsh or corrosive in tone; "an acerbic tone piercing
       otherwise flowery prose"; "a barrage of acid comments"; "her
       acrid remarks make her many enemies"; "bitter words";
       "blistering criticism"; "caustic jokes about political
       assassination, talk-show hosts and medical ethics"; "a
       sulfurous denunciation"; "a vitriolic critique" [syn:
       acerb, acerbic, acid, acrid, bitter, blistering,
       caustic, sulfurous, sulphurous, virulent,
       vitriolic]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "acerbic":
   acerb, acerbate, acescent, acetose, acid, acidic, acidulent,
   acidulous, acrid, acrimonious, amaroidal, asperous, astringent,
   biting, bitter, bitter as gall, burning, caustic, choleric, coarse,
   corroding, corrosive, crab, crabbed, cutting, dry, embittered,
   escharotic, green, hard, harsh, incisive, irritating, keen,
   mordacious, mordant, nose-tickling, penetrating, pickled, piercing,
   piquant, poignant, pungent, rancorous, rankled, resentful,
   resenting, rough, scathing, scorching, sec, severe, sharp, sore,
   sour, sour as vinegar, soured, sourish, splenetic, stabbing,
   stewing, stinging, tart, tartish, trenchant, unripe, unsweet,
   unsweetened, vinegarish, vinegary, virulent, vitriolic,
   withering