Be sulky (4)
I believe the answer is:
mope
'be sulky' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mope that I've seen before include "Move listlessly and aimlessly" , "Brood over a poem" , "Yield to low spirits with an odd poem" , "Hang about moodily over poem" , "Sulk over poem." .)