observer vs expert

observer and expert both are nouns.

Word	Noun	Adjective	Verb	Adverb
observer	Yes	No	No	No
expert	Yes	Yes	No	No

As nouns, expert is a hypernym of observer; that is, expert is a word with a broader meaning than observer:

observer (noun)	expert (noun)
a person who becomes aware (of things or events) through the senses	a person with special knowledge or ability who performs skillfully
an expert who observes and comments on something

observer (adjective)	expert (adjective)
	having or showing knowledge and skill and aptitude
	of or relating to or requiring special knowledge to be understood