private security force vs watcher

private security force and watcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
private security force	Yes	No	No	No
watcher	Yes	No	No	No

private security force (noun)	watcher (noun)
a privately employed group hired to protect the security of a business or industry	a guard who keeps watch
	a close observer; someone who looks at something (such as an exhibition of some kind)
	a person who keeps a devotional vigil by a sick bed or by a dead body