Safe after a struggle to truss enemy up, relax (4,3)
I believe the answer is:
ease off
'relax' is the definition.
(both can mean to reduce in intensity)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ease off that I've seen before include "Slacken gradually" , "Slow down" , "Let up" , "Throttle back" , "Put the brake on" .)