burial vault vs sepulture

burial vault and sepulture both are nouns.

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

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

Other hypernyms of burial vault include burial chamber, sepulcher, sepulchre.

burial vault (noun)	sepulture (noun)
a burial chamber (usually underground)	a chamber that is used as a grave
	the ritual placing of a corpse in a grave