Source : Webster's Revised Unabridged Dictionary (1913)

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.

            His fierce thunder drove us to the deep. --Milton.

   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.

            The fierce foe hung upon our broken rear. --Milton.

            Thou huntest me as a fierce lion.     --Job. x. 16.

   3. Excessively earnest, eager, or ardent.

   Syn: Ferocious; savage; cruel; vehement; impetuous;
        barbarous; fell. See {Ferocious}. -- {Fierce"ly}, adv.
        -- {Fierce"ness}, n.

Source : WordNet®

fiercely
     adv 1: in a physically fierce manner; "silence broken by dogs
            barking ferociously"; "they fought fiercely" [syn: {ferociously}]
     2: in an emotionally fierce manner; "she was fiercely proud of
        her children"