foster-daughter vs fosterling

foster-daughter and fosterling both are nouns.

Word	Noun	Adjective	Verb	Adverb
foster-daughter	Yes	No	No	No
fosterling	Yes	No	No	No

As nouns, fosterling is a hypernym of foster-daughter; that is, fosterling is a word with a broader meaning than foster-daughter:

foster-daughter: someone who is raised as a daughter although not related by birth
fosterling: a child who is raised by foster parents

Other hypernyms of foster-daughter include foster-child, foster child.

foster-daughter (noun)	fosterling (noun)
someone who is raised as a daughter although not related by birth	a child who is raised by foster parents