To set free, amputate limb? (5)
I believe the answer is:
unpeg
'to set free' is the definition.
(unpeg can mean to release or unfasten)
'amputate limb?' is the wordplay.
'amputate' becomes 'un' (I can't justify this - if you can you should believe this answer much more).
'limb?' becomes 'peg' (peg is a kind of limb).
'un'+'peg'='UNPEG'
(Other definitions for unpeg that I've seen before include "free" , "Detach" , "no longer freeze" , "Take down from the line" , "Remove (clothes from a washing line)" .)