The Collaborative International Dictionary of English v.0.48:

Convictive \Con*vict"ive\, a.
   Convincing. [R.]
   [1913 Webster]

         The best and most convictive argument.   --Glanwill.
   -- Con*vict"ive*ly, adv. -- Con*vict"ive*ness, n.
   [1913 Webster]