Lewis & Short

conjectūrālis, e, adj. [conjectura], belonging to conjecture or guessing, conjectural: ars medicina, Cels. 1 praef.; 2, 6 fin.
Esp. freq. in rhet. lang.: causa, Cic. Top. 24, 92: causae, id. ib. 11, 50; Quint. 2, 4, 26: status, id. 3, 6, 29; and subst.: con-jectūrālĭa, ium, n., conjectures: haec, Quint. 7, 1, 53; 4, 4, 8.
Adv.: conjec-tūrālĭter, conjeclurally, by conjecture: nil conjecturaliter gestum, nil per ambages, Sid. Ep. 8, 11 fin.