Source : Webster's Revised Unabridged Dictionary (1913)

Legitimacy \Le*git"i*ma*cy\ (-[i^]*m[.a]*s[y^]), n. [See
   {Legitimate}, a.]
   The state, or quality, of being legitimate, or in conformity
   with law; hence, the condition of having been lawfully
   begotten, or born in wedlock.

         The doctrine of Divine Right, which has now come back
         to us, like a thief from transportation, under the
         alias of Legitimacy.                     --Macaulay.

Source : WordNet®

legitimacy
     n 1: lawfulness by virtue of being authorized or in accordance
          with law [ant: {illegitimacy}]
     2: undisputed credibility [syn: {authenticity}, {genuineness}]