The Collaborative International Dictionary of English v.0.48:

Apposite \Ap"po*site\, a. [L. appositus, p. p. of apponere to
   set or put to; ad + ponere to put, place.]
   Very applicable; well adapted; suitable or fit; relevant;
   pat; -- followed by to; as, this argument is very apposite to
   the case. -- Ap"po*site*ly, adv. -- Ap"po*site*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

appositeness
    n 1: appropriateness for the occasion; "the phrase had
         considerable aptness" [syn: aptness, appositeness]
         [ant: inappositeness, inaptness]