cub vs boy

cub and boy both are nouns.

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

As nouns, boy is a hypernym of cub; that is, boy is a word with a broader meaning than cub:

Other hypernyms of cub include male child.

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

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