The Collaborative International Dictionary of English v.0.48:

Arrogance \Ar"ro*gance\, n. [F., fr. L. arrogantia, fr.
   arrogans. See Arrogant.]
   The act or habit of arrogating, or making undue claims in an
   overbearing manner; that species of pride which consists in
   exorbitant claims of rank, dignity, estimation, or power, or
   which exalts the worth or importance of the person to an
   undue degree; proud contempt of others; lordliness;
   haughtiness; self-assumption; presumption.
   [1913 Webster]

         I hate not you for her proud arrogance.  --Shak.
   [1913 Webster]

   Syn: Haughtiness; hauteur; assumption; lordliness;
        presumption; pride; disdain; insolence; conceit;
        conceitedness. See Haughtiness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

arrogance
    n 1: overbearing pride evidenced by a superior manner toward
         inferiors [syn: arrogance, haughtiness, hauteur,
         high-handedness, lordliness]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "arrogance":
   airs, assurance, assuredness, audacity, belief, bluster,
   boastfulness, bold front, boldness, brash bearing, brashness,
   brassiness, bravado, brazenness, bumptiousness, certitude,
   cheekiness, clannishness, cliquishness, cockiness, cocksureness,
   conceit, confidence, confidentness, contempt, contemptuousness,
   contumely, conviction, courage, daring, daringness, defial,
   defiance, defying, derision, despite, disdain, disdainfulness,
   disparagement, disregard, effrontery, egotism, exclusiveness, face,
   faith, gall, hardihood, haughtiness, hauteur, hubris, impertinence,
   impudence, independence, insolence, insult, loftiness, morgue,
   nerve, obtrusiveness, overconfidence, oversureness, overweening,
   overweeningness, pardonable pride, pertness, poise, pomposity,
   pompousness, positiveness, presumption, presumptuousness,
   pretension, pretentiousness, pride, pridefulness, procacity,
   proudness, purse-pride, pushiness, ridicule, sauciness, scorn,
   scornfulness, security, self-assertion, self-assurance,
   self-confidence, self-consequence, self-esteem, self-importance,
   self-reliance, self-respect, self-sufficiency, settled belief,
   side, sniffiness, snobbery, snobbishness, snootiness, snottiness,
   sovereign contempt, stiff-necked pride, stiff-neckedness,
   subjective certainty, superciliousness, sureness, surety,
   toploftiness, trust, uppishness, uppityness, vanity