watcher vs spotter

watcher and spotter both are nouns.

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

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

watcher (noun)	spotter (noun)
a guard who keeps watch	someone who is the first to observe something
a close observer; someone who looks at something (such as an exhibition of some kind)	a worker employed to apply spots (as markers or identifiers)
a person who keeps a devotional vigil by a sick bed or by a dead body	a worker employed at a dry-cleaning establishment to remove spots
	a person employed to keep watch for some anticipated event