Very long online movie? (4)
I believe the answer is:
epic
'very long' is the definition.
(I've seen this before)
'online movie?' is the wordplay.
'online' becomes 'e' (as in e-mail or e-commerce).
'movie?' becomes 'pic' (abbreviation for picture**).
'e'+'pic'='EPIC'
(Other definitions for epic that I've seen before include "Exodus, say" , "Long poem telling of great events" , "Long narrative poem telling of a hero's deeds" , "imposing" , "eg The Iliad" .)