The Collaborative International Dictionary of English v.0.48:

Audacity \Au*dac"i*ty\, n.
   1. Daring spirit, resolution, or confidence; venturesomeness.
      [1913 Webster]

            The freedom and audacity necessary in the commerce
            of men.                               --Tatler.
      [1913 Webster]

   2. Reckless daring; presumptuous impudence; -- implying a
      contempt of law or moral restraints.
      [1913 Webster]

            With the most arrogant audacity.      --Joye.
      [1913 Webster]

WordNet (r) 3.0 (2006):

audacity
    n 1: fearless daring [syn: audacity, audaciousness,
         temerity]
    2: aggressive boldness or unmitigated effrontery; "he had the
       audacity to question my decision" [syn: audacity,
       audaciousness]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "audacity":
   adventuresomeness, adventurousness, arrogance, assurance,
   audaciousness, balls, bold front, boldness, brash bearing,
   brashness, brass, brassiness, bravado, bravura, brazenness,
   brinkmanship, bumptiousness, cheek, cheekiness, cockiness,
   contempt, contemptuousness, contumely, courage, courage fou,
   courting disaster, daredevilry, daredeviltry, daring, daringness,
   defial, defiance, defying, derision, derring-do, despite, disdain,
   disregard, effrontery, enterprise, face, fire-eating,
   flirting with death, foolhardiness, forwardness, gall,
   going for broke, hardihood, hardiness, harebrainedness, hubris,
   impertinence, impudence, insolence, mettle, nerve, obtrusiveness,
   overboldness, overweening, overweeningness, pertness,
   playing with fire, presumption, presumptuousness, procacity,
   pushiness, resolution, sauciness, spirit, uppishness, uppityness,
   venturesomeness, venturousness