pupil vs auditor

pupil and auditor both are nouns.

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

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

pupil (noun)	auditor (noun)
the contractile aperture in the center of the iris of the eye; resembles a large black dot	a qualified accountant who inspects the accounting records and practices of a business or other organization
a learner who is enrolled in an educational institution	someone who listens attentively
a young person attending school (up through senior high school)	a student who attends a course but does not take it for credit