boy vs sonny

boy and sonny both are nouns.

Word	Noun	Adjective	Verb	Adverb
boy	Yes	No	No	No
sonny	Yes	No	No	No

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

boy (noun)	sonny (noun)
a youthful male person	a male child (a familiar term of address to a boy)
(ethnic slur) offensive and disparaging term for Black man
a friendly informal reference to a grown man
a male human offspring