The Collaborative International Dictionary of English v.0.48:

Acrimonious \Ac"ri*mo"ni*ous\, a. [Cf. LL. acrimonious, F.
   acrimonieux.]
   1. Acrid; corrosive; as, acrimonious gall. [Archaic]
      --Harvey.
      [1913 Webster]

   2. Caustic; bitter-tempered' sarcastic; as, acrimonious
      dispute, language, temper.
      [1913 Webster]

WordNet (r) 3.0 (2006):

acrimonious
    adj 1: marked by strong resentment or cynicism; "an acrimonious
           dispute"; "bitter about the divorce" [syn: acrimonious,
           bitter]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "acrimonious":
   acerb, acerbate, acerbic, acid, acidic, acidulent, acidulous,
   acrid, astringent, belligerent, biting, bitter, burning, caustic,
   choleric, contentious, corroding, corrosive, cranky, cross,
   cutting, double-edged, edged, embittered, escharotic, fierce,
   harsh, incisive, indignant, irascible, irate, ireful, keen, mad,
   mordacious, mordant, penetrating, piercing, poignant, quarrelsome,
   rancorous, rankled, resentful, resenting, rigorous, rough,
   scathing, scorching, severe, sharp, sore, splenetic, stabbing,
   stewing, stinging, strident, stringent, tart, testy, trenchant,
   vehement, violent, virulent, vitriolic, withering, wrathful,
   wrathy, wroth