Epic journey (7)
I believe the answer is:
odyssey
'epic journey' is the definition.
(journey taken by Odysseus)
This is the entire clue.
(Other definitions for odyssey that I've seen before include "Epic poem - epic voyage" , "A long adventurous journey - see Homer" , "Homer's epic poem" , "Greek epic on the wanderings of Ulysses" , "Homerian epic" .)