The Collaborative International Dictionary of English v.0.48:

Ardent \Ar"dent\, a. [OE. ardaunt, F. ardant, p. pr. of arder to
   burn, fr. L. ardere.]
   1. Hot or burning; causing a sensation of burning; fiery; as,
      ardent spirits, that is, distilled liquors; an ardent
      fever.
      [1913 Webster]

   2. Having the appearance or quality of fire; fierce; glowing;
      shining; as, ardent eyes. --Dryden.
      [1913 Webster]

   3. Warm, applied to the passions and affections; passionate;
      fervent; zealous; vehement; as, ardent love, feelings,
      zeal, hope, temper.
      [1913 Webster]

            An ardent and impetuous race.         --Macaulay.
      [1913 Webster]

   Syn: Burning; hot; fiery; glowing; intense; fierce; vehement;
        eager; zealous; keen; fervid; fervent; passionate;
        affectionate.
        [1913 Webster]

WordNet (r) 3.0 (2006):

ardent
    adj 1: characterized by intense emotion; "ardent love"; "an
           ardent lover"; "a fervent desire to change society"; "a
           fervent admirer"; "fiery oratory"; "an impassioned
           appeal"; "a torrid love affair" [syn: ardent,
           fervent, fervid, fiery, impassioned, perfervid,
           torrid]
    2: characterized by strong enthusiasm; "ardent revolutionaries";
       "warm support" [syn: ardent, warm]
    3: glowing or shining like fire; "from rank to rank she darts
       her ardent eyes"- Alexander Pope; "frightened by his ardent
       burning eyes"

Moby Thesaurus II by Grady Ward, 1.0:

231 Moby Thesaurus words for "ardent":
   abandoned, ablaze, acquiescent, afire, aflame, aflicker, aglow,
   agog, agreeable, alacritous, alcoholic, alight, amative, amatory,
   amenable, amorous, and, anxious, assiduous, athirst, avid, baking,
   blazing, blistering, boiling, boiling over, breathless, broiling,
   burning, burning hot, candent, candescent, canicular, comburent,
   committed, compliant, conflagrant, consenting, constant, content,
   cooperative, cordial, crying, dedicated, delirious, desirous,
   devoted, devout, diligent, disposed, docile, drunk, eager, earnest,
   ebullient, emphatic, energetic, enthusiastic, erotic, excited,
   exciting, extreme, exuberant, fain, faithful, fanatic, favorable,
   favorably disposed, favorably inclined, febrile, fervent, fervid,
   fevered, feverish, fierce, fiery, flagrant, flaming, flaring,
   flickering, flushed, forward, fuming, game, genial, glowing, great,
   grilling, guttering, hard, hard-core, hardworking, hasty, hearty,
   heated, hectic, hospitable, hot, hot as fire, hot as hell,
   hot-blooded, hotheaded, ignescent, ignited, impassioned, impatient,
   impetuous, importunate, impulsive, in a blaze, in a glow,
   in earnest, in flames, in the mind, in the mood, incandescent,
   inclined, indefatigable, industrious, inflamed, insistent, intense,
   intent, intent on, intoxicated, keen, kindled, laborious,
   lascivious, liege, like a furnace, like an oven, live, lively,
   living, loverlike, loverly, loyal, madcap, mighty, minded,
   never idle, on fire, overheated, overwarm, parching, passionate,
   perfervid, piping hot, pliant, powerful, precipitate, predisposed,
   prompt, prone, provoking, quick, ready, ready and willing,
   receptive, red-hot, reeking, relentless, resolute, responsive,
   roasting, scalding, scintillant, scintillating, scorching, searing,
   sedulous, seething, serious, sexual, simmering, sincere, sizzling,
   sizzling hot, sleepless, smoking, smoking hot, smoldering,
   sparking, spirited, spirituous, staunch, steadfast, steaming,
   steamy, stimulating, stirring, strenuous, strong, sudorific,
   sweating, sweaty, sweltering, sweltry, thirsty, tireless, toasting,
   torrid, totally committed, tractable, true, uncontrolled,
   unextinguished, unflagging, ungoverned, unquenched, unremitting,
   unrestrained, unsleeping, unsparing, unwearied, urgent, vehement,
   vigorous, vinous, warm, warmhearted, well-disposed, well-inclined,
   white-hot, willed, willing, willinghearted, winy, with a kick,
   zealous