boy vs Jr

boy and Jr both are nouns.

Word	Noun	Adjective	Verb	Adverb
boy	Yes	No	No	No
Jr	Yes	No	No	No

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

Other hyponyms of boy include Jnr, Junior, mama's boy, mamma's boy, mother's boy.

boy (noun)	Jr (noun)
a youthful male person	a son who has the same first name as his father
(ethnic slur) offensive and disparaging term for Black man
a friendly informal reference to a grown man
a male human offspring