parent vs foster

parent is a noun but foster is not a noun.

Word	Noun	Adjective	Verb	Adverb
parent	Yes	No	Yes	No
foster	No	Yes	Yes	No

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

Other hyponyms of parent include fledge, cradle.

parent (noun)	foster (noun)
an organism (plant or animal) from which younger ones are obtained
a father or mother; one who begets or one who gives birth to or nurtures and raises a child; a relative who plays the role of guardian

parent (adjective)	foster (adjective)
	providing or receiving nurture or parental care though not related by blood or legal ties

parent (verb)	foster (verb)
look after a child until it is an adult	help develop, help grow
	promote the growth of
	bring up under fosterage; of children