Source : Webster's Revised Unabridged Dictionary (1913)

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

   2. Lacking discernment; injudicious; ignorant.

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

Source : WordNet®

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