boy vs cub

boy and cub both are nouns.

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

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

boy (noun)	cub (noun)
a youthful male person	the young of certain carnivorous mammals such as the bear or wolf or lion
(ethnic slur) offensive and disparaging term for Black man	a male child (a familiar term of address to a boy)
a friendly informal reference to a grown man	an awkward and inexperienced youth
a male human offspring

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