noun
dangerous weapon; lethal weapon; murder weapon
Refers to any object used or intended to cause death or serious injury, especially in criminal contexts. Can also be used figuratively.
犯人は凶器を持って逃走した。
The suspect fled carrying a weapon.
警察は現場から凶器を押収した。
The police seized the murder weapon from the scene.
武器 is a general term for weapons, including those used in warfare or self-defense. 凶器 specifically implies a weapon used in a crime or capable of causing death.
凶 (bad luck, disaster, evil) + 器 (container, utensil). The combination literally means 'instrument of evil' and has been used to refer to weapons used in violent crimes.