boy vs Junior

boy and Junior both are nouns.

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

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

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

boy (noun)	Junior (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

boy (adjective)	Junior (adjective)
	used of the younger of two persons of the same name especially used to distinguish a son from his father