tombstone vs memorial

tombstone and memorial both are nouns.

Word	Noun	Adjective	Verb	Adverb
tombstone	Yes	No	No	No
memorial	Yes	No	No	No

As nouns, memorial is a hypernym of tombstone; that is, memorial is a word with a broader meaning than tombstone:

Other hypernyms of tombstone include monument, stone.

tombstone (noun)	memorial (noun)
a stone that is used to mark a grave	a structure erected to commemorate persons or events
	a recognition of meritorious service
	a written statement of facts submitted in conjunction with a petition to an authority