☉ 铜墙铁壁 【tónɡqiánɡtiěbì】
　　[ bastion of iron,impregnable fortress as a wall of bronze impregnable like walls of brass and iron ] 亦作“铁壁铜墙”，比喻防御工事坚固，也比喻力量的强大、意志的坚定。