The Collaborative International Dictionary of English v.0.48:

Expertness \Ex*pert"ness\, n.
   Skill derived from practice; readiness; as, expertness in
   seamanship, or in reasoning.

   Syn: Facility; readiness; dexterity; adroitness; skill. See
        Facility.
        [1913 Webster]

WordNet (r) 3.0 (2006):

expertness
    n 1: skillfulness by virtue of possessing special knowledge
         [syn: expertness, expertise]