foster parent vs guardian

foster parent and guardian both are nouns.

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

As nouns, guardian is a hypernym of foster parent; that is, guardian is a word with a broader meaning than foster parent:

foster parent: a person who acts as parent and guardian for a child in place of the child's natural parents but without legally adopting the child
guardian: a person who cares for persons or property

Other hypernyms of foster parent include defender, protector, shielder.

foster parent (noun)	guardian (noun)
a person who acts as parent and guardian for a child in place of the child's natural parents but without legally adopting the child	a person who cares for persons or property