observer vs auditor

observer and auditor both are nouns.

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

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

observer: a person who becomes aware (of things or events) through the senses
auditor: someone who listens attentively

observer (noun)	auditor (noun)
a person who becomes aware (of things or events) through the senses	a qualified accountant who inspects the accounting records and practices of a business or other organization
an expert who observes and comments on something	someone who listens attentively
	a student who attends a course but does not take it for credit