Opinatio, onis, f. g. Verbale. Cicer.A thenking: au vncertaine iudgement: a supposing or weening.Opinationem volunt este imbecillam assensionem.Cic.
Lewis and Short: Latin dictionary
ŏpīnātĭo, ōnis, f. [id.], a supposing, opining; a supposition, conjecture, imagination, fancy, opinion, belief (class.): opinationem volunt esse imbecillam assensionem, Cic. Tusc. 4, 7, 15; id. Ac. 2, 25, 78: haec autem opinatio est judicatio se scire, quod nesciat, id. Tusc. 4, 11, 26; cf. the context: mordax et inepta, Val. Max. 1, 8, 8: (Tullius) quid super tali opinatione sentiret, Arn. 3, 6.