Impressive online image? (4)
I believe the answer is:
epic
'impressive' is the definition.
(I've seen this before)
'online image?' is the wordplay.
'online' becomes 'e' (as in e-mail or e-commerce).
'image?' becomes 'pic' (I've seen this in other clues).
'e'+'pic'='EPIC'
(Other definitions for epic that I've seen before include "eg Beowulf" , "Long poem telling of heroic events" , "Larger than life" , "blockbuster" , "Ben Hur, say" .)