Source : Webster's Revised Unabridged Dictionary (1913)

Elusive \E*lu"sive\, a.
   Tending to elude; using arts or deception to escape; adroitly
   escaping or evading; eluding the grasp; fallacious.

         Elusive of the bridal day, she gives Fond hopes to all,
         and all with hopes deceives.             --Pope.
   -- {E*lu"sive*ly}, adv. -- {E*lu"sive*ness}, n.

Source : WordNet®

elusiveness
     n : the quality of being difficult to grasp or pin down; "the
         author's elusiveness may at times be construed as
         evasiveness"