A large limb creates panic (5)
I believe the answer is:
alarm
'panic' is the definition.
(alarm can mean panic or fear)
'a large limb' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'limb' becomes 'arm' (arm is a kind of limb).
'a'+'l'+'arm'='ALARM'
'creates' acts as a link.
(Other definitions for alarm that I've seen before include "Anxious awareness of danger" , "with which many awake to in the morning" , "Tocsin" , "Burglar deterrent" , "Put the wind up" .)