Meaning

adjective immune to attack; incapable of being tampered with

adjective capable of conceiving

adjective incapable of being overcome, challenged or refuted

originFrom Late Middle English imprenable, impregnable (“impossible to capture, impregnable”), from Old French imprenable (modern French imprenable (“impregnable”)), from im- (a variant of in- (prefix meaning ‘not’) + prenable (“(military) of a building, position, etc.: takable”) (from prendre (“to take”) + -able (suffix meaning ‘creating an effect or influence’)). Prendre is derived from Latin…

Etymology from Wiktionary, CC BY-SA 3.0