Greek muse of epic poetry (8)
I believe the answer is:
calliope
'greek muse of epic poetry' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for calliope that I've seen before include "something powered by steam" , "Greek Muse of eloquence and epic poetry, or a kind of organ" , "Steam organ: Muse of epic poetry" , "source of inspiration?" , "One Muse" .)