Lewis & Short

ŏpīnābĭlis, e, adj. [opinor], that rests on opinion or conjecture; conjectural, imaginary (class.): hanc omnem partem rerum opinabilem appellabant, Cic. Ac. 1, 8, 31; cited ap. Non. 148, 26: artes, quae conjecturā continentur et sunt opinabiles, Cic. Div. 1, 14, 24: mediocritates, id. Tusc. 3, 31, 74 (opp. naturales): amor (opp. naturalis), Gell. 12, 1, 23.