headstone vs memorial

headstone and memorial both are nouns.

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

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

Other hypernyms of headstone include monument, stone.

headstone (noun)	memorial (noun)
the central building block at the top of an arch or vault	a structure erected to commemorate persons or events
a stone that is used to mark a grave	a recognition of meritorious service
	a written statement of facts submitted in conjunction with a petition to an authority