铜墙铁壁 tóngqiángtiěbì impregnable defense Origin Definitions Defs Strokes Stroke Words Sentences Sents 铜 銅 tóng noun copper copper (chemical element Cu); also used to refer to bronze and other copper alloys墙 牆 qiáng noun wall a wall or similar barrier built of brick, stone, or other materials铁 鐵 tiě noun iron iron (Fe); the metal used for making steel and tools壁 bì noun wall wall; partition