Close forcefully (4)
I believe the answer is:
slam
'close forcefully' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slam that I've seen before include "Shut loudly and forcibly" , "If it's grand, it wins all 13 tricks in bridge game" , "big contract" , "Shut (door) with force" , "Ambitious contract" .)