sepulture vs tomb

sepulture and tomb both are nouns.

Word	Noun	Adjective	Verb	Adverb
sepulture	Yes	No	No	No
tomb	Yes	No	No	No

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

sepulture: a chamber that is used as a grave
tomb: a place for the burial of a corpse (especially beneath the ground and marked by a tombstone)

Other hypernyms of sepulture include chamber, grave.

sepulture (noun)	tomb (noun)
a chamber that is used as a grave	a place for the burial of a corpse (especially beneath the ground and marked by a tombstone)
the ritual placing of a corpse in a grave