foster-child vs nipper

foster-child and nipper both are nouns.

Word	Noun	Adjective	Verb	Adverb
foster-child	Yes	No	No	No
nipper	Yes	No	No	No

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

Other hypernyms of foster-child include child, fry, kid, minor, nestling, shaver, small fry, tiddler, tike, tyke, youngster.

foster-child (noun)	nipper (noun)
a child who is raised by foster parents	a grasping structure on the limb of a crustacean or other arthropods
	a young person of either sex