son vs Jr

son and Jr both are nouns.

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

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

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

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