The Collaborative International Dictionary of English v.0.48:

Impudence \Im"pu*dence\ ([i^]m"p[-u]*dens), n. [L. impudentia:
   cf. F. impudence. See Impudent.]
   The quality of being impudent; assurance, accompanied with a
   disregard of the presence or opinions of others;
   shamelessness; forwardness; lack of modesty.
   [1913 Webster]

         Clear truths that their own evidence forces us to
         admit, or common experience makes it impudence to deny.
                                                  --Locke.
   [1913 Webster]

         Where pride and impudence (in fashion knit)
         Usurp the chair of wit.                  --B. Jonson.

   Syn: Shamelessness; audacity; insolence; effrontery;
        sauciness; impertinence; pertness; rudeness.

   Usage: Impudence, Effrontery, Sauciness. Impudence
          refers more especially to the feelings as manifested
          in action. Effrontery applies to some gross and public
          exhibition of shamelessness. Sauciness refers to a
          sudden pert outbreak of impudence, especially from an
          inferior. Impudence is an unblushing kind of
          impertinence, and may be manifested in words, tones,
          gestures, looks, etc. Effrontery rises still higher,
          and shows a total or shameless disregard of duty or
          decorum under the circumstances of the case. Sauciness
          discovers itself toward particular individuals, in
          certain relations; as in the case of servants who are
          saucy to their masters, or children who are saucy to
          their teachers. See Impertinent, and Insolent.
          [1913 Webster]

WordNet (r) 3.0 (2006):

impudence
    n 1: an impudent statement [syn: impudence, cheek,
         impertinence]
    2: the trait of being rude and impertinent; inclined to take
       liberties [syn: crust, gall, impertinence, impudence,
       insolence, cheekiness, freshness]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "impudence":
   arrogance, audacity, back talk, backchat, bold front, boldness,
   brash bearing, brashness, brass, brassiness, bravado,
   brazen boldness, brazenfacedness, brazenness, bumptiousness, cheek,
   cheekiness, chutzpah, cockiness, contempt, contemptuousness,
   daring, daringness, defial, defiance, defying, derision, despite,
   discourtesy, disdain, disesteem, dishonor, disparagement,
   disregard, disrespect, disrespectfulness, effrontery,
   face of brass, flippancy, freshness, gall, guff, hardihood,
   heroics, hubris, impertinence, impoliteness, improvidence,
   imprudence, incivility, indiscretion, injudiciousness, insolence,
   irreverence, lack of respect, lip, mouth, overboldness,
   overcarelessness, overconfidence, oversureness, overweeningness,
   pertness, presumption, presumptuousness, rashness, ridicule,
   rudeness, sauce, sauciness, shamelessness, side, temerariousness,
   temerity, unchariness, unwariness