memorial vs epitaph

memorial and epitaph both are nouns.

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

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

Other hyponyms of memorial include festschrift.

memorial (noun)	epitaph (noun)
a structure erected to commemorate persons or events	an inscription on a tombstone or monument in memory of the person buried there
a recognition of meritorious service	a summary statement of commemoration for a dead person
a written statement of facts submitted in conjunction with a petition to an authority