irrătĭōnābĭlis (inr-), e, adj.,
without reason , irrational (post-class.; not in Quint., v. Spald. ad Quint. 2, 16, 16): error, Ap. Dogm. Plat. p. 21: motus, Amm. 31, 12, 15.— Of musical intervals, = logica, proportional , harmonic : irrationabilia (sunt) quibus non subest ratio, Mart. Cap. 9, § 949.—Subst.: irrătĭōnābĭlĭa , ĭum, n., unreasoning creatures , Lact. 2, 2, 17.— Adv.: irrătĭōnābĭlĭter , irrationally , Amm. 19, 10, 1; Tert. Poen. 2; Cael. Aur. Acut. 2, 37, 199.