铁壁 tiěbì impregnable defense Origin Definitions Defs Strokes Stroke Words Sentences Sents 铜墙铁壁 tóngqiángtiěbì impregnable defense (idiom) copper wall and iron bastion; used to describe an extremely solid and indestructible fortification or defense铁壁铜墙 tiěbìtóngqiáng impregnable fortress an extremely strong and solid fortification; an unbreakable defense