[1] : The Collaborative International Dictionary of English v.0.48

fierce \fierce\, a. compar. fiercer; superl. fiercest.
   oe. fers, fiers, of. fier, nom. fiers, fierce, savage,
   cruel, f. fier proud, from l. ferus wild, savage, cruel;
   perh. akin to e. bear the animal. cf. feral, ferocity.
   1. furious; violent; unrestrained; impetuous; as, a fierce
      wind.
      1913 webster

            his fierce thunder drove us to the deep. --milton.
      1913 webster

   2. vehement in anger or cruelty; ready or eager to kill or
      injure; of a nature to inspire terror; ferocious. "a
      fierce whisper." --dickens. "a fierce tyrant." --pope.
      1913 webster

            the fierce foe hung upon our broken rear. --milton.
      1913 webster

            thou huntest me as a fierce lion.     --job. x. 16.
      1913 webster

   3. excessively earnest, eager, or ardent.

   syn: ferocious; savage; cruel; vehement; impetuous;
        barbarous; fell. see ferocious. -- fierce"ly, adv.
        -- fierce"ness, n.
        1913 webster
see also:
fiercer fiercest feral ferocity ferocious fierce"ly 
fierce"ness 

[2] : WordNet (r) 2.0

fierce
     adj 1: marked by extreme and violent energy; "a ferocious beating";
            "fierce fighting"; "a furious battle" syn: ferocious,
             furious, savage
     2: marked by extreme intensity of emotions or convictions;
        inclined to react violently; fervid; "fierce loyalty"; "in
        a tearing rage"; "vehement dislike"; "violent passions"
        syn: tearing, vehement, violent, trigger-happy
     3: ruthless in competition; "cutthroat competition"; "bowelless
        readiness to take advantage" syn: cutthroat, bowelless
     4: violently agitated and turbulent; "boisterous winds and
        waves"; "the fierce thunders roar me their music"- ezra
        pound; "rough weather"; "rough seas" syn: boisterous, rough
see also:
ferocious furious savage tearing vehement violent 
trigger-happy cutthroat bowelless boisterous rough 

[3] : Moby Thesaurus II by Grady Ward, 1.0

227 moby thesaurus words for "fierce":
   draconian, tartarean, abandoned, acid, acidulous, acrid,
   acrimonious, acute, aggressive, amok, angry, animal, antagonistic,
   anthropophagous, astringent, atrocious, awful, barbaric, barbarous,
   battling, beastly, bellicose, belligerent, bellowing, berserk,
   bestial, biting, bitter, bloodthirsty, bloody, bloody-minded,
   brutal, brutalized, brute, brutish, cannibalistic, carried away,
   caustic, chauvinist, chauvinistic, combative, concentrated,
   contentious, cruel, cruel-hearted, cutting, dangerous, delirious,
   demoniac, demoniacal, desperate, devilish, diabolic, dire,
   distracted, double-edged, drastic, dreadful, ecstatic, edged,
   enemy, enraged, enraptured, escharotic, excessive, exorbitant,
   exquisite, extravagant, extreme, fell, feral, ferine, ferocious,
   fiendish, fiendlike, fiery, fighting, fighting mad, frantic,
   frenzied, full of fight, fulminating, fuming, furious, great, grim,
   haggard, harsh, hawkish, hellish, hog-wild, homicidal, hopping mad,
   hostile, hotheaded, howling, hysterical, immoderate, impetuous,
   in a rage, in a transport, in hysterics, incisive, infernal,
   infuriate, infuriated, inhuman, inhumane, inimical, inordinate,
   intemperate, intense, intoxicated, intractable, jingo, jingoish,
   jingoist, jingoistic, keen, kill-crazy, mad, maddened, madding,
   malign, malignant, maniac, martial, menacing, merciless, militant,
   militaristic, military, mordacious, mordant, murderous,
   noncivilized, offensive, orgasmic, orgiastic, outrageous,
   passionate, penetrating, piercing, pitiless, poignant, possessed,
   pugnacious, quarrelsome, rabid, racking, raging, ramping, ranting,
   raving, raving mad, ravished, rigorous, roaring, roaring mad,
   rough, running mad, ruthless, saber-rattling, sadistic, sanguinary,
   sanguineous, satanic, savage, scathing, scrappy, severe, sharkish,
   sharp, simmering, slavering, soldierlike, soldierly, splitting,
   stabbing, stinging, storming, stormy, strident, stringent,
   subhuman, superlative, supreme, tameless, tart, tempestuous,
   terrible, threatening, tigerish, tornadic, tough, transcendent,
   transported, trenchant, trigger-happy, truculent, tumultuous,
   turbulent, unchristian, uncivilized, unconscionable,
   uncontrollable, unfriendly, ungentle, unhuman, unpacific,
   unpeaceable, unpeaceful, untamed, vehement, venomous, vicious,
   violent, virulent, vitriolic, volcanic, warlike, warmongering,
   warring, wild, wild-eyed, wild-looking, wolfish

Fierce >> F Words
Fierce, definition of term: Fierce
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