Honors English III Vocabulary Practice Test

Impregnable describes a fortress that cannot be taken by force. It means the defenses are so strong that an assault would be unable to breach them, making capture effectively impossible. The other words point to the opposite idea: vulnerable means easy to attack or damage, penetrable means something that can be entered, and fragile means easily broken. So impregnable best fits the concept of an unconquerable fortification. For example, a fortress with imposing walls, formidable fortifications, and strategic defenses might be described as impregnable.