spotter vs watcher

spotter and watcher both are nouns.

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

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

Other hypernyms of spotter include security guard, watchman.

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