A long poem in The Pictorial (4)
I believe the answer is:
epic
'a long poem' is the definition.
(I've seen this before)
'in the pictorial' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EPIC' is hidden within 'the pictorial'.
(Other definitions for epic that I've seen before include "Large-scale" , "On a grand scale, like heroic poem" , "Marathon" , "Heroic; saga" , "Exodus, say" .)