spent shell casing; empty cartridge
Refers to the metal casing left after a bullet has been fired. Used in military, shooting, and forensic contexts.
Spent shell casings were scattered around the shooting range.
Compound of 空 (kara, 'empty') and 薬莢 (yakkyō, 'cartridge case'). The reading やっきょう is a euphonic change from やくきょう.