potter's field vs necropolis

potter's field and necropolis both are nouns.

Word	Noun	Adjective	Verb	Adverb
potter's field	Yes	No	No	No
necropolis	Yes	No	No	No

As nouns, necropolis is a hypernym of potter's field; that is, necropolis is a word with a broader meaning than potter's field:

Other hypernyms of potter's field include burial ground, burial site, burying ground, cemetery, graveyard, memorial park.

potter's field (noun)	necropolis (noun)
a cemetery for unknown or indigent people	a tract of land used for burials