The Collaborative International Dictionary of English v.0.48:

Effrontery \Ef*front"er*y\, n.; pl. Effronteries. [F.
   effronterie, fr. effront['e] shameless, fr. L. effrons,
   -ontis, putting forth the forehead, i. e., barefaced,
   shameless; ex + frons the forehead. See Front.]
   Impudence or boldness in confronting or in transgressing the
   bounds of duty or decorum; insulting presumptuousness;
   shameless boldness; barefaced assurance.
   [1913 Webster]

         Corruption lost nothing of its effrontery. --Bancroft.

   Syn: Impudence; sauciness. See Impudence.
        [1913 Webster]

WordNet (r) 3.0 (2006):

effrontery
    n 1: audacious (even arrogant) behavior that you have no right
         to; "he despised them for their presumptuousness" [syn:
         presumption, presumptuousness, effrontery,
         assumption]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "effrontery":
   arrogance, assurance, audacity, boldness, brashness, brass,
   brazenness, bumptiousness, cheek, confidence, contumely, crust,
   face, gall, hardihood, hubris, impertinence, impudence, insolence,
   nerve, obtrusiveness, overweening, overweeningness, presumption,
   presumptuousness, procacity, pushiness, self-assurance,
   self-confidence, temerity, uppishness, uppityness