boy vs Jnr

boy and Jnr both are nouns.

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

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

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

boy (noun)	Jnr (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