patroller vs watcher

patroller and watcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
patroller	Yes	No	No	No
watcher	Yes	No	No	No

As nouns, watcher is a hypernym of patroller; that is, watcher is a word with a broader meaning than patroller:

patroller: someone on patrol duty; an individual or a member of a group that patrols an area
watcher: a guard who keeps watch

Other hypernyms of patroller include security guard, watchman.

patroller (noun)	watcher (noun)
someone on patrol duty; an individual or a member of a group that patrols an area	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