The Collaborative International Dictionary of English v.0.48:

Opine \O*pine"\, v. t. & i. [imp. & p. p. Opined; p. pr. & vb.
   n. Opining.] [L. opinari, p. p. opinatus; akin to opinus
   (in comp.) thinking, and perh. to E. apt: cf. F. opiner.]
   To have an opinion; to judge; to think; to suppose. --South.
   [1913 Webster]

WordNet (r) 3.0 (2006):

opine
    v 1: express one's opinion openly and without fear or
         hesitation; "John spoke up at the meeting" [syn: opine,
         speak up, speak out, animadvert, sound off]
    2: expect, believe, or suppose; "I imagine she earned a lot of
       money with her new novel"; "I thought to find her in a bad
       state"; "he didn't think to find her in the kitchen"; "I
       guess she is angry at me for standing her up" [syn: think,
       opine, suppose, imagine, reckon, guess]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "opine":
   account, account as, adjudge, adjudicate, allow, allude to, assume,
   be afraid, be judicious, believe, blurt, blurt out,
   call attention to, comment, conceive, conclude, consider, count,
   daresay, deduce, deem, divine, dream, esteem, estimate, exclaim,
   exercise judgment, expect, express an opinion, fancy, feel,
   form an opinion, gather, grant, guess, have a hunch, have an idea,
   have an impression, have an inkling, have the idea, hold, hold as,
   imagine, infer, interject, judge, let, let be, let drop, let fall,
   look upon as, maintain, make reference to, mention, muse, note,
   observe, pine, prefigure, presume, presuppose, presurmise,
   provisionally accept, reckon, refer to, reflect, regard, remark,
   repute, say, set down as, speak, suppose, surmise, suspect, take,
   take for, take for granted, take it, take to be, think, think of,
   trow, understand, view as, ween