The Collaborative International Dictionary of English v.0.48:

Opinionative \O*pin"ion*a*tive\, a.
   1. Unduly attached to one's own opinions; opinionated.
      --Milton.
      [1913 Webster]

   2. Of the nature of an opinion; conjectured. [Obs.] "Things
      both opinionative and practical." --Bunyan. --
      O*pin"ion*a*tive*ly, adv. -- O*pin"ion*a*tive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

opinionative
    adj 1: obstinate in your opinions [syn: opinionated,
           opinionative, self-opinionated]