The Collaborative International Dictionary of English v.0.48:

Validity \Va*lid"i*ty\, n. [Cf. F. validit['e], L. validitas
   strength.]
   [1913 Webster]
   1. The quality or state of being valid; strength; force;
      especially, power to convince; justness; soundness; as,
      the validity of an argument or proof; the validity of an
      objection.
      [1913 Webster]

   2. (Law) Legal strength, force, or authority; that quality of
      a thing which renders it supportable in law, or equity;
      as, the validity of a will; the validity of a contract,
      claim, or title.
      [1913 Webster]

   3. Value. [Obs.] "Rich validity." --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

validity
    n 1: the quality of being valid and rigorous [syn: cogency,
         validity, rigor, rigour]
    2: the quality of having legal force or effectiveness [syn:
       validity, validness]
    3: the property of being strong and healthy in constitution
       [syn: robustness, hardiness, lustiness, validity]