The Collaborative International Dictionary of English v.0.48:

Insolent \In"so*lent\, a. [F. insolent, L. insolens, -entis,
   pref. in- not + solens accustomed, p. pr. of solere to be
   accustomed.]
   [1913 Webster]
   1. Deviating from that which is customary; novel; strange;
      unusual. [Obs.]
      [1913 Webster]

            If one chance to derive any word from the Latin
            which is insolent to their ears . . . they forthwith
            make a jest at it.                    --Pettie.
      [1913 Webster]

            If any should accuse me of being new or insolent.
                                                  --Milton.
      [1913 Webster]

   2. Haughty and contemptuous or brutal in behavior or
      language; overbearing; domineering; grossly rude or
      disrespectful; saucy; as, an insolent master; an insolent
      servant. "A paltry, insolent fellow." --Shak.
      [1913 Webster]

            Insolent is he that despiseth in his judgment all
            other folks as in regard of his value, of his
            cunning, of his speaking, and of his bearing.
                                                  --Chaucer.
      [1913 Webster]

            Can you not see? or will ye not observe . . .
            How insolent of late he is become,
            How proud, how peremptory?            --Shak.
      [1913 Webster]

   3. Proceeding from or characterized by insolence; insulting;
      as, insolent words or behavior.
      [1913 Webster]

            Their insolent triumph excited . . . indignation.
                                                  --Macaulay.

   Syn: Overbearing; insulting; abusive; offensive; saucy;
        impudent; audacious; pert; impertinent; rude;
        reproachful; opprobrious.

   Usage: Insolent, Insulting. Insolent, in its primitive
          sense, simply denoted unusual; and to act insolently
          was to act in violation of the established rules of
          social intercourse. He who did this was insolent; and
          thus the word became one of the most offensive in our
          language, indicating gross disregard for the feelings
          of others. Insulting denotes a personal attack, either
          in words or actions, indicative either of scorn or
          triumph. Compare Impertinent, Affront,
          Impudence.
          [1913 Webster]

WordNet (r) 3.0 (2006):

insolent
    adj 1: marked by casual disrespect; "a flip answer to serious
           question"; "the student was kept in for impudent
           behavior" [syn: impudent, insolent, snotty-nosed,
           flip]
    2: unrestrained by convention or propriety; "an audacious trick
       to pull"; "a barefaced hypocrite"; "the most bodacious
       display of tourism this side of Anaheim"- Los Angeles Times;
       "bald-faced lies"; "brazen arrogance"; "the modern world with
       its quick material successes and insolent belief in the
       boundless possibilities of progress"- Bertrand Russell [syn:
       audacious, barefaced, bodacious, bald-faced,
       brassy, brazen, brazen-faced, insolent]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "insolent":
   abusive, arrogant, assuming, atrocious, audacious, aweless,
   backhand, backhanded, bold, brash, brassy, brazen, brazenfaced,
   bumptious, callous, calumnious, cavalier, challenging, cheeky,
   cocky, cold, contemptuous, contumelious, cool, crude, daring,
   defiant, defying, degrading, derisive, dictatorial, discourteous,
   disdainful, disparaging, disregardful, disrespectful, familiar,
   forward, fresh, greatly daring, hard, hardened, haughty,
   high-and-mighty, hubristic, humiliating, impenitent, imperative,
   impertinent, impolite, improvident, imprudent, impudent, inaffable,
   incautious, indiscreet, injudicious, insubordinate, insulting,
   irreverent, left-handed, lofty, magisterial, obdurate, obtrusive,
   offensive, outrageous, overbearing, overbold, overcareless,
   overconfident, overpresumptuous, oversure, overweening, peremptory,
   pert, presuming, presumptuous, procacious, pushy, rash,
   regardless of consequences, ridiculing, rude, saucy, scurrile,
   scurrilous, self-appointed, self-elect, supercilious, superior,
   temerarious, unabject, unaccommodating, unchary, uncivil,
   uncomplaisant, uncontrite, uncourteous, uncourtly, ungallant,
   ungracious, unmelted, unpolite, unrepentant, unrepenting,
   unsoftened, unspeakable, untouched, unwary, uppish, uppity, wise,
   would-be