Impenetrabilis, & hoc impenetrabile pe. cor. Li. That cannot be piersed or entred: impenetrable.Armis impenetrabilis.Stat.Mens impenetrabilis iræ. Sil. A minde that anger cannot enrer into.Pudicitia impenetrabilis. Tac. Vnuincible chastitie.Impenetrabilis ferro silex. Liuius. A flint that Iron cannot pierce.Tergus ad scuta galeasque impenetrabile. Flini. An hyde to make targates and helmets so strong that they cannot be piercen.
Lewis and Short: Latin dictionary
impĕnĕtrābĭlis (inp-), e, adj. [2. inpenetrabilis], that cannot be penetrated, impenetrable (perh. not ante-Aug.). I.Lit.: silex ferro, Liv. 36, 25: superior pars corporis crocodili (with dura), Sen. Q. N. 4, 2 med.; cf.: tergus hippopotami ad scuta, Plin. 8, 25, 39, 95: congeries imbribus, id. 8, 36, 54, 127: cruppellarii accipiendis ictibus, Tac. A. 3, 43: quae impenetrabilia quaeque pervia, id. ib. 12, 35.—II.Trop., that cannot be overcome, unconquerable, unyielding: patet impenetrabilis ille Luctibus, Sil. 6, 413: impenetrabilis blanditiis, Sen. Q. N. 4 praef.: mens irae, Sil. 7, 561: pudicitia Agrippinae, Tac. A. 4, 12.