Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
conclusive [kənˈkluːsɪv] adj (evidence) неопровержи́мый/неопровержи́м (defeat) оконча́тельный*оконча́телен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.