son vs Junior

son and Junior both are nouns.

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

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

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

son (noun)	Junior (noun)
a male human offspring	a son who has the same first name as his father

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