im·preg·na·ble / imˈpreg-nəbəl/ • adj. (of a fortified position) unable to be captured or broken into: an impregnable wall of solid sandstone | fig. the companies are impregnable to takeovers. ∎  unable to be defeated or destroyed; unassailable: the case against Hastings would have been almost impregnable.DERIVATIVES: im·preg·na·bil·i·ty / -ˌpregnəˈbilitē/ n.im·preg·na·bly / -blē/ adv.

impregnable XV (imprenable). — (O)F. imprenable, f. IM-2 + prenable takeable, f. pren-, stem of prendre take :- L. prehendere; see -ABLE. The later forms impre(i)gnable, which depend upon OF. vars., induced the pronunc. with g.