master-at-arms (plural masters-at-arms)
- (UK, Navy) A warrant officer or chief petty officer responsible for discipline aboard a naval ship.
- (UK, Army) A commissioned officer responsible for overseeing all fitness training in subordinate units.
- (US, Navy) A petty officer responsible for law enforcement, antiterrorism, force protection, and expeditionary warfare.
- An officer in a fraternal or similar organization charged with maintaining order.