The Collaborative International Dictionary of English v.0.48:

Willful \Will"ful\, a. [Will + full.] [Written also wilful.]
   [1913 Webster]
   1. Of set purpose; self-determined; voluntary; as, willful
      murder. --Foxe.
      [1913 Webster]

            In willful poverty chose to lead his life.
                                                  --Chaucer.
      [1913 Webster]

            Thou to me
            Art all things under heaven, all places thou,
            Who, for my willful crime, art banished hence.
                                                  --Milton.
      [1913 Webster]

   2. Governed by the will without yielding to reason;
      obstinate; perverse; inflexible; stubborn; refractory; as,
      a willful man or horse.
      [1913 Webster] -- Will"ful*ly, adv. -- Will"ful*ness,
      n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

willful
    adj 1: done by design; "the insult was intentional"; "willful
           disobedience" [syn: willful, wilful]
    2: habitually disposed to disobedience and opposition [syn:
       froward, headstrong, self-willed, willful, wilful]