watcher vs watchman

watcher and watchman both are nouns.

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

As nouns, watcher and watchman are synonyms defined as:

Other synonyms of watcher include security guard.

watcher (noun)	watchman (noun)
a guard who keeps watch	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