Source : Webster's Revised Unabridged Dictionary (1913)

Skillful \Skill"ful\, a. [Written also skilful.]
   1. Discerning; reasonable; judicious; cunning. [Obs.] ``Of
      skillful judgment.'' --Chaucer.

   2. Possessed of, or displaying, skill; knowing and ready;
      expert; well-versed; able in management; as, a skillful
      mechanic; -- often followed by at, in, or of; as, skillful
      at the organ; skillful in drawing.

            And they shall call the husbandman to mourning, and
            such as are skillful of lamentations to wailing.
                                                  --Amos v. 16.

   Syn: Expert; skilled; dexterous; adept; masterly; adroit;
        clever; cunning. -- {Skill"ful*ly}, adv. --
        {Skill"ful*ness}, n.

Source : WordNet®

skillfulness
     n : the state of being cognitively skillful [ant: {unskillfulness}]