epic vs heroic meter

epic and heroic meter both are nouns.

Word	Noun	Adjective	Verb	Adverb
epic	Yes	Yes	No	No
heroic meter	Yes	No	No	No

As nouns, heroic meter is a hyponym of epic; that is, heroic meter is a word with a more specific, narrower meaning than epic:

epic: a long narrative poem telling of a hero's deeds
heroic meter: a verse form suited to the treatment of heroic or elevated themes; dactylic hexameter or iambic pentameter

Other hyponyms of epic include chanson de geste, rhapsody, heroic, heroic verse.

epic (noun)	heroic meter (noun)
a long narrative poem telling of a hero's deeds	a verse form suited to the treatment of heroic or elevated themes; dactylic hexameter or iambic pentameter

epic (adjective)	heroic meter (adjective)
constituting or having to do with or suggestive of a literary epic
very imposing or impressive; surpassing the ordinary (especially in size or scale)