a person who keeps watch over something or someone

a privately employed group hired to protect the security of a business or industry

be vigilant, be on the lookout or be careful

a security guard at a bank

(during World War II in Britain) someone whose duty was to watch for fires caused by bombs dropped from the air

a person employed to keep watch for some anticipated event

a watchman who works during the night

someone on patrol duty; an individual or a member of a group that patrols an area

a privately employed group hired to protect the security of a business or industry