The Collaborative International Dictionary of English v.0.48:

Wilful \Wil"ful\, a., Wilfully \Wil"ful*ly\, adv., Wilfulness
\Wil"ful*ness\, n.
   See Willful, Willfully, and Willfulness.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wilfully
    adv 1: in a willful manner; "she had willfully deceived me"
           [syn: willfully, wilfully]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

WILFULLY, intentionally.
     2. In charging certain offences it is required that they should be
stated to be wilfully done. Arch. Cr. Pl. 51, 58; Leach's Cr. L. 556.
     3. In Pennsylvania it has been decided that the word maliciously was an
equivalent for the word wilfully, in an indictment for arson. 5 Whart. R.
427.