pupil vs catechumen

pupil and catechumen both are nouns.

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

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

pupil: a learner who is enrolled in an educational institution
catechumen: a new convert being taught the principles of Christianity by a catechist

pupil (noun)	catechumen (noun)
the contractile aperture in the center of the iris of the eye; resembles a large black dot	a new convert being taught the principles of Christianity by a catechist
a learner who is enrolled in an educational institution
a young person attending school (up through senior high school)