The Collaborative International Dictionary of English v.0.48:

Dissuasive \Dis*sua"sive\, a.
   Tending to dissuade or divert from a measure or purpose;
   dehortatory; as, dissuasive advice. -- n. A dissuasive
   argument or counsel; dissuasion; dehortation. --Prynne. --
   Dis*sua"sive*ly, adv.
   [1913 Webster]