pupil vs aperture

pupil and aperture both are nouns.

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

As nouns, aperture is a hypernym of pupil; that is, aperture is a word with a broader meaning than pupil:

pupil: the contractile aperture in the center of the iris of the eye; resembles a large black dot
aperture: a natural opening in something

pupil (noun)	aperture (noun)
the contractile aperture in the center of the iris of the eye; resembles a large black dot	an man-made opening; usually small
a learner who is enrolled in an educational institution	a device that controls amount of light admitted
a young person attending school (up through senior high school)	a natural opening in something