lettering vs epitaph

lettering and epitaph both are nouns.

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

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

lettering: letters inscribed (especially words engraved or carved) on something
epitaph: an inscription on a tombstone or monument in memory of the person buried there

Other hyponyms of lettering include superscription, epigraph.

lettering (noun)	epitaph (noun)
letters inscribed (especially words engraved or carved) on something	an inscription on a tombstone or monument in memory of the person buried there
	a summary statement of commemoration for a dead person