It could kill you to let go when on limb! (7)
I believe the answer is:
firearm
'it could kill you' is the definition.
The definition suggests a singular noun which matches the answer.
'let go when on limb' is the wordplay.
'let go' becomes 'fire' (both can mean to dismiss from a job).
'when on' says to put letters next to each other.
'limb' becomes 'arm' (arm is a kind of limb).
'fire'+'arm'='FIREARM'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for firearm that I've seen before include "Lethal Weapon" , "piece" , "Hand-held weapon" , "Pistol, rifle or gun" , "Colt perhaps" .)