Cleave, split (5)
I believe the answer is:
sever
This clue is a double definition.
'cleave' is the first definition.
(I've seen this in another clue)
'split' is the second definition.
(sever can mean to split or separate)
(Other definitions for sever that I've seen before include "Cut off, separate" , "Cut completely" , "Lop off" , "Detach" , "Put an end to (connection or relationship)" .)