Source : Webster's Revised Unabridged Dictionary (1913)

Corroboratory \Cor*rob"o*ra*to*ry\ (-t?-r?), a.
   Tending to strengthen; corroborative; as, corroboratory
   facts.

Source : WordNet®

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