The Collaborative International Dictionary of English v.0.48:

Flippant \Flip"pant\, a. [Prov. E. flip to move nimbly; cf. W.
   llipa soft, limber, pliant, or Icel. fleipa to babble,
   prattle. Cf. Flip, Fillip, Flap, Flipper.]
   1. Of smooth, fluent, and rapid speech; speaking with ease
      and rapidity; having a voluble tongue; talkative.
      [1913 Webster]

            It becometh good men, in such cases, to be flippant
            and free in their speech.             --Barrow.
      [1913 Webster]

   2. Speaking fluently and confidently, without knowledge or
      consideration; empty; trifling; inconsiderate; pert;
      petulant. "Flippant epilogues." --Thomson.
      [1913 Webster]

            To put flippant scorn to the blush.   --I. Taylor.
      [1913 Webster]

            A sort of flippant, vain discourse.   --Burke.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flippant \Flip"pant\, n.
   A flippant person. [R.] --Tennyson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flippant
    adj 1: showing inappropriate levity [syn: flippant, light-
           minded]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "flippant":
   airy, bantering, belittling, biggety, bluff, booing, brash, brazen,
   careless, casual, catcalling, chaffing, cheeky, chutzpadik, cocky,
   contemptuous, crusty, cursory, degage, derisive, derisory,
   discourteous, dismissive, disregardant, disregardful,
   disrespectful, easygoing, facetious, facy, fleering, flip, fooling,
   forgetful, free and easy, fresh, frivolous, gally, gratuitous,
   grinning, heedless, hissing, hooting, impertinent, impudent,
   inconsiderate, indifferent, insolent, insouciant, irreverent,
   jeering, jocular, joshing, kidding, lazy, leering, light-hearted,
   malapert, mocking, nervy, oblivious, offhand, offhanded, panning,
   perfunctory, pert, quizzical, ragging, railing, rallying, razzing,
   reckless, regardless, respectless, ridiculing, roasting, rude,
   sassy, saucy, scoffing, scornful, shallow, smart, smart-alecky,
   smart-ass, smirking, sneering, snickering, sniggering, snorting,
   supercilious, superficial, tactless, taunting, teasing,
   thoughtless, twitting, uncalled-for, undiplomatic, unheedful,
   unheeding, unmindful, unprepared, unready, unserious, unsolicitous,
   untactful, unthinking, wise-ass