boy vs one of the boys

boy and one of the boys both are nouns.

Word	Noun	Adjective	Verb	Adverb
boy	Yes	No	No	No
one of the boys	Yes	No	No	No

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

boy: a friendly informal reference to a grown man
one of the boys: a man who has been socially accepted into a group of other men

Other hyponyms of boy include broth of a boy, broth of a man.

boy (noun)	one of the boys (noun)
a youthful male person	a man who has been socially accepted into a group of other men
(ethnic slur) offensive and disparaging term for Black man
a friendly informal reference to a grown man
a male human offspring