Source : Webster's Revised Unabridged Dictionary (1913)

Proviso \Pro*vi"so\, n.; pl. {Provisos}. [L., (it) being
   provided, abl. of provisus, p. p. of providere. See
   {Provide}, and cf. {Purview}.]
   An article or clause in any statute, agreement, contract,
   grant, or other writing, by which a condition is introduced,
   usually beginning with the word provided; a conditional
   stipulation that affects an agreement, contract, law, grant,
   or the like; as, the contract was impaired by its proviso.

         He doth deny his prisoners, But with proviso and
         exception.                               --Shak.

Source : WordNet®

proviso
     n : a stipulated condition; "he accepted subject to one
         provision" [syn: {provision}]
     [also: {provisoes} (pl)]