pupil vs day boarder

pupil and day boarder both are nouns.

Word	Noun	Adjective	Verb	Adverb
pupil	Yes	No	No	No
day boarder	Yes	No	No	No

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

pupil: a young person attending school (up through senior high school)
day boarder: a schoolchild at a boarding school who has meals at school but sleeps at home

Other hyponyms of pupil include boarder, latchkey child, schoolboy.

pupil (noun)	day boarder (noun)
the contractile aperture in the center of the iris of the eye; resembles a large black dot	a schoolchild at a boarding school who has meals at school but sleeps at home
a learner who is enrolled in an educational institution
a young person attending school (up through senior high school)