Im·preg·na·ble a. Not to be stormed, or taken by assault; incapable of being subdued; able to resist attack; unconquerable; as, an impregnable fortress; impregnable virtue.
The man's affection remains wholly unconcerned and impregnable. --South.
-- Im*preg*na*ble*ness, n. -- Im*preg*na*bly, adv.