The Collaborative International Dictionary of English v.0.48:

Extravagant \Ex*trav"a*gant\, a. [F. extravagant, fr. L. extra
   on the outside + vagans, -antis, p. pr. of vagari to wander,
   from vagus wandering, vague. See Vague.]
   1. Wandering beyond one's bounds; roving; hence, foreign.
      [Obs.]
      [1913 Webster]

            The extravagant and erring spirit hies
            To his confine.                       --Shak.
      [1913 Webster]

   2. Exceeding due bounds; wild; excessive; unrestrained; as,
      extravagant acts, wishes, praise, abuse.
      [1913 Webster]

            There appears something nobly wild and extravagant
            in great natural geniuses.            --Addison.
      [1913 Webster]

   3. Profuse in expenditure; prodigal; wasteful; as, an
      extravagant man. "Extravagant expense." --Bancroft.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Extravagant \Ex*trav"a*gant\, n.
   1. One who is confined to no general rule. --L'Estrange.
      [1913 Webster]

   2. pl. (Eccl. Hist.) Certain constitutions or decretal
      epistles, not at first included with others, but
      subsequently made a part of the canon law.
      [1913 Webster]

WordNet (r) 3.0 (2006):

extravagant
    adj 1: unrestrained, especially with regard to feelings;
           "extravagant praise"; "exuberant compliments";
           "overweening ambition"; "overweening greed" [syn:
           excessive, extravagant, exuberant, overweening]
    2: recklessly wasteful; "prodigal in their expenditures" [syn:
       extravagant, prodigal, profligate, spendthrift]

Moby Thesaurus II by Grady Ward, 1.0:

321 Moby Thesaurus words for "extravagant":
   Babylonian, Corinthian, Gothic, a bit much, abandoned, abounding,
   absurd, abundant, acute, affluent, aggrandized, all-sufficing,
   ample, amplified, aplenty, awe-inspiring, awful, ballyhooed,
   barbaric, baroque, beyond belief, bibulous, big, bigoted, bizarre,
   blatant, bombastic, bottomless, boundless, bounteous, bountiful,
   brain-born, brazen, brazenfaced, cockamamie, colorful, copious,
   costly, crapulent, crapulous, crazy, crude, cutthroat, cutting,
   dear, deluxe, diffuse, diffusive, disproportionate, dissipative,
   dizzy, drastic, dream-built, easy come, easy go, effuse, effusive,
   egregious, elaborate, elegant, enormous, epidemic, exacting,
   exaggerated, excessive, exhaustless, exorbitant, expensive,
   extortionate, extreme, extremist, exuberant, fabulous, fanatic,
   fanciful, fancy, fancy-born, fancy-built, fancy-woven, fantasque,
   fantastic, fat, fecund, fertile, fierce, fine, flagrant,
   flamboyant, flaring, flashy, flaunting, florid, flush, foolish,
   formless, full, furious, galore, garish, gassy, gaudy, generous,
   gigantic, glaring, glorious, gluttonous, gorgeous, gouging, grand,
   grandiloquent, grandiose, great, grossly overpriced, grotesque,
   gushing, gushy, haggard, high, high-flown, high-sounding,
   high-swelling, highfalutin, highfaluting, hyperbolic,
   hypertrophied, immoderate, implausible, imposing, impractical,
   impressive, improvident, in plenty, in quantity, incontinent,
   incredible, indulgent, inexhaustible, inflated, inflationary,
   inordinate, intemperate, intense, irrational, laughable, lavish,
   liberal, loud, ludicrous, lurid, luxuriant, luxurious, maggoty,
   magnificent, magnified, majestic, many, maximal, meretricious,
   monstrous, much, noble, nonsensical, notional, numerous, obtrusive,
   opulent, ornate, ostentatious, out of bounds, out of sight,
   outlandish, outrageous, outre, overbig, overdeveloped, overdone,
   overdrawn, overemphasized, overemphatic, overenthusiastic,
   overestimated, overflowing, overgenerous, overgreat, overgrown,
   overindulgent, overindulging, overlarge, overlavish, overliberal,
   overmuch, overpraised, overpriced, overreligious, oversold,
   overstated, overstressed, overweening, overwrought, overzealous,
   palatial, penny-wise and pound-foolish, perfervid, piercing,
   plenitudinous, plenteous, plentiful, plenty, pleonastic, plush,
   poppycockish, posh, pound-foolish, preposterous, pretentious,
   prevailing, prevalent, princely, prodigal, productive, profligate,
   profuse, profusive, prohibitive, prolific, proud, puffed, rabid,
   rampant, reckless, redundant, reiterative, repetitive, replete,
   rich, ridiculous, rife, rigorous, riotous, ritzy, rococo, rough,
   running over, screaming, self-indulgent, sensational, severe,
   shameless, sharp, showy, silly, skyrocketing, spectacular,
   spendthrift, spiraling, splendacious, splendid, splendiferous,
   splitting, stately, steep, stiff, stretched, sumptuous,
   superabundant, superb, superfancy, superfine, superlative, swank,
   swanky, swell, swinish, swollen, tall, tautologous, tawdry,
   teeming, too much, tough, touted, towering, ultrazealous,
   unbalanced, unbridled, unconscionable, unconstrained, uncontrolled,
   undeserved, undisciplined, undue, unfrugal, unjustifiable,
   unjustified, unlimited, unmeasurable, unmeasured, unreasonable,
   unrestrained, unthrifty, unwarranted, usurious, vehement, venomous,
   violent, virulent, vulgar, wasteful, wealthy, weird, well-found,
   well-furnished, well-provided, well-stocked, whimsical, wholesale,
   wild, wild-eyed, wild-looking, windy, zealotic