mamma's boy vs son

mamma's boy and son both are nouns.

Word	Noun	Adjective	Verb	Adverb
mamma's boy	Yes	No	No	No
son	Yes	No	No	No

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

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

Other hypernyms of mamma's boy include boy.

mamma's boy (noun)	son (noun)
a boy excessively attached to his mother; lacking normal masculine interests	a male human offspring