From 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.