His place in the hearts of most Thai is central and impregnable.
When Sherman reached those earthworks, he thought them the most impregnable he had ever seen.
She claimed he groped her crotch, pulling at her pantyhose, but the barrier was impregnable.
early 15c., imprenable "impossible to capture," from Middle French imprenable "invulnerable," from assimilated form of in- "not, opposite of" (see in- (1)) + Old French prenable "assailable, vulnerable" (see pregnable). With intrusive -g- 16c., on model of deign, reign, etc. Related: Impregnability.