onlooker vs looker

onlooker and looker both are nouns.

Word	Noun	Adjective	Verb	Adverb
onlooker	Yes	No	No	No
looker	Yes	No	No	No

As nouns, looker is a hypernym of onlooker; that is, looker is a word with a broader meaning than onlooker:

onlooker: someone who looks on
looker: a close observer; someone who looks at something (such as an exhibition of some kind)

Other hypernyms of onlooker include spectator, viewer, watcher, witness.

onlooker (noun)	looker (noun)
someone who looks on	a very attractive or seductive looking woman
	a close observer; someone who looks at something (such as an exhibition of some kind)