cub vs sonny boy

cub and sonny boy both are nouns.

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

As nouns, cub and sonny boy are synonyms defined as:

Other synonyms of cub include lad, laddie, sonny.

cub (noun)	sonny boy (noun)
the young of certain carnivorous mammals such as the bear or wolf or lion	a male child (a familiar term of address to a boy)
a male child (a familiar term of address to a boy)
an awkward and inexperienced youth

cub (verb)	sonny boy (verb)
give birth to cubs