The Collaborative International Dictionary of English v.0.48:

Unwonted \Un*wont"ed\ ([u^]n*w[u^]nt"[e^]d), a.
   1. Not wonted; unaccustomed; unused; not made familiar by
      practice; as, a child unwonted to strangers. --Milton.
      [1913 Webster]

   2. Uncommon; unusual; infrequent; rare; as, unwonted changes.
      "Unwonted lights." --Byron.
      [1913 Webster] -- Un*wont"ed*ly, adv. --
      Un*wont"ed*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unwontedly
    adv 1: in an unusual manner