Source : Webster's Revised Unabridged Dictionary (1913)

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}.

Source : WordNet®

expertness
     n : skillfulness by virtue of possessing special knowledge [syn:
          {expertise}]