watcher vs lookout man

watcher and lookout man both are nouns.

Word	Noun	Adjective	Verb	Adverb
watcher	Yes	No	No	No
lookout man	Yes	No	No	No

As nouns, lookout man is a hyponym of watcher; that is, lookout man is a word with a more specific, narrower meaning than watcher:

watcher (noun)	lookout man (noun)
a guard who keeps watch	a person employed to keep watch for some anticipated event
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