Source : Webster's Revised Unabridged Dictionary (1913)

Confirmative \Con*firm"a*tive\, a. [L. confirmativus: cf. F.
   confirmatif.]
   Tending to confirm or establish. --Sherwood. --
   {Con*firm"a*tive*ly}, adv.

Source : WordNet®

confirmative
     adj : serving to support or corroborate; "collateral evidence"
           [syn: {collateral}, {confirming}, {confirmatory}, {corroborative},
            {corroboratory}, {substantiating}, {substantiative}, {validating},
            {validatory}, {verificatory}, {verifying}]