birth vs cub

birth and cub both are nouns.

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

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

birth (noun)	cub (noun)
the event of being born	the young of certain carnivorous mammals such as the bear or wolf or lion
a baby born; an offspring	a male child (a familiar term of address to a boy)
the process of giving birth	an awkward and inexperienced youth
the kinship relation of an offspring to the parents
the time when something begins (especially life)

birth (verb)	cub (verb)
cause to be born	give birth to cubs