tomb vs mastaba

tomb and mastaba both are nouns.

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

As nouns, mastaba is a hyponym of tomb; that is, mastaba is a word with a more specific, narrower meaning than tomb:

tomb: a place for the burial of a corpse (especially beneath the ground and marked by a tombstone)
mastaba: an ancient Egyptian mud-brick tomb with a rectangular base and sloping sides and flat roof

Other hyponyms of tomb include burial chamber, sepulcher, sepulchre, sepulture, mastabah.

tomb (noun)	mastaba (noun)
a place for the burial of a corpse (especially beneath the ground and marked by a tombstone)	an ancient Egyptian mud-brick tomb with a rectangular base and sloping sides and flat roof