Study all night (4)
I believe the answer is:
cram
'study all night' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cram that I've seen before include "Pack in or study hard" , "prepare hastily for the paper" , "Stuff full" , "Stuff (facts for exam)" , "Swot (for exam)" .)