unpenetrable Synonyms

dense inviolable invulnerable resistant uninjectable impenetrable for impervious to break-ins impossible to crack fortified against break-ins invulnerable to break-ins protected against break-ins resistant to break-ins invincible insurmountable immutable impassable impenetrable impermeable impervious impossible impracticable impregnable inaccessible indestructible indomitable secure against break-ins