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.