Let up on (4)
I believe the answer is:
ease
'let up on' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ease that I've seen before include "Lessen intensity" , "Comfort and naturalness" , "'Comfort, rest (4)'" , "Become less severe; facilitate" , "soldier may be at it" .)