The Collaborative International Dictionary of English v.0.48:

Unskillful \Un*skill"ful\, a. [Spelt also unskilful.]
   [1913 Webster]
   1. Not skillful; inexperienced; awkward; bungling; as, an
      unskillful surgeon or mechanic; an unskillful logician.
      [1913 Webster]

   2. Lacking discernment; injudicious; ignorant.
      [1913 Webster]

            Though it make the unskillful laugh, can not but
            make the judicious grieve.            --Shak.
      [1913 Webster] -- Un*skill"ful*ly, adv. --
      Un*skill"ful*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unskillfulness
    n 1: a lack of cognitive skill [ant: skillfulness]