The Collaborative International Dictionary of English v.0.48:

Defiant \De*fi"ant\, a. [Cf. F. d['e]fiant, p. pr. of d['e]fier.
   See Defy.]
   Full of defiance; bold; insolent; as, a defiant spirit or
   act.
   [1913 Webster]

         In attitude stern and defiant.           --Longfellow.
   -- De*fi"ant*ly, adv. -- De*fi"ant*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

defiantly
    adv 1: in a rebellious manner; "he rejected her words
           rebelliously" [syn: rebelliously, contumaciously,
           defiantly]