family vs foster family

family and foster family both are nouns.

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

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

family (noun)	foster family (noun)
primary social group; parents and children	the family of a fosterling
people descended from a common ancestor
a social unit living together
(biology) a taxonomic group containing one or more genera
a collection of things sharing a common attribute
an association of people who share common beliefs or activities
a loose affiliation of gangsters in charge of organized criminal activities
a person having kinship with another or others