watchman, watcher, security guard

a guard who keeps watch

• bank guard — a security guard at a bank
• fire watcher — (during World War II in Britain) someone whose duty was to watch for fires caused by bombs dropped from the air
• lookout, lookout man, sentinel, sentry, watch, spotter, scout, picket — a person employed to watch for something to happen
• night watchman — a watchman who works during the night
• patroller — someone on patrol duty; an individual or a member of a group that patrols an area
• portwatcher — a watchman on a wharf

• guard — a person who keeps watch over something or someone

• security force, private security force — a privately employed group hired to protect the security of a business or industry