epigraph vs inscription

epigraph and inscription both are nouns.

Word	Noun	Adjective	Verb	Adverb
epigraph	Yes	No	No	No
inscription	Yes	No	No	No

As nouns, inscription is a hypernym of epigraph; that is, inscription is a word with a broader meaning than epigraph:

epigraph: an engraved inscription
inscription: letters inscribed (especially words engraved or carved) on something

Other hypernyms of epigraph include lettering.

epigraph (noun)	inscription (noun)
an engraved inscription	the activity of inscribing (especially carving or engraving) letters or words
a quotation at the beginning of some piece of writing	letters inscribed (especially words engraved or carved) on something
	a short message (as in a book or musical work or on a photograph) dedicating it to someone or something