mother's boy vs boy

mother's boy and boy both are nouns.

Word	Noun	Adjective	Verb	Adverb
mother's boy	Yes	No	No	No
boy	Yes	No	No	No

As nouns, boy is a hypernym of mother's boy; that is, boy is a word with a broader meaning than mother's boy:

mother's boy: a boy excessively attached to his mother; lacking normal masculine interests
boy: a male human offspring

Other hypernyms of mother's boy include son.

mother's boy (noun)	boy (noun)
a boy excessively attached to his mother; lacking normal masculine interests	a youthful male person
	(ethnic slur) offensive and disparaging term for Black man
	a friendly informal reference to a grown man
	a male human offspring