cub vs bear cub

cub and bear cub both are nouns.

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

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

cub: the young of certain carnivorous mammals such as the bear or wolf or lion
bear cub: a young bear

Other hyponyms of cub include lion cub, tiger cub.

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

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