columbarium vs burial vault

columbarium and burial vault both are nouns.

Word	Noun	Adjective	Verb	Adverb
columbarium	Yes	No	No	No
burial vault	Yes	No	No	No

As nouns, burial vault is a hypernym of columbarium; that is, burial vault is a word with a broader meaning than columbarium:

columbarium: a sepulchral vault or other structure having recesses in the walls to receive cinerary urns
burial vault: a burial chamber (usually underground)

Other hypernyms of columbarium include vault.

columbarium (noun)	burial vault (noun)
a sepulchral vault or other structure having recesses in the walls to receive cinerary urns	a burial chamber (usually underground)
a niche for a funeral urn containing the ashes of the cremated dead
a birdhouse for pigeons