eyewitness vs watcher

eyewitness and watcher both are nouns.

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

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

eyewitness: a spectator who can describe what happened
watcher: a close observer; someone who looks at something (such as an exhibition of some kind)

Other hypernyms of eyewitness include looker, spectator, viewer, witness.

eyewitness (noun)	watcher (noun)
a spectator who can describe what happened	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

eyewitness (verb)	watcher (verb)
be present at an event and see it with one's own eyes