citation vs epigraph

citation and epigraph both are nouns.

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

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

Other hyponyms of citation include mimesis, misquotation, misquote, agraphon.

citation (noun)	epigraph (noun)
an official award (as for bravery or service) usually given as formal public statement	an engraved inscription
a short note recognizing a source of information or of a quoted passage	a quotation at the beginning of some piece of writing
a summons that commands the appearance of a party at a proceeding
a passage or expression that is quoted or cited
(law) the act of citing (as of spoken words or written passages or legal precedents etc.)