epos vs heroic verse

epos and heroic verse both are nouns.

Word	Noun	Adjective	Verb	Adverb
epos	Yes	No	No	No
heroic verse	Yes	No	No	No

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

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

Other hyponyms of epos include chanson de geste, rhapsody, heroic, heroic meter.

epos (noun)	heroic verse (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
a body of poetry that conveys the traditions of a society by treating some epic theme