Tin with a power to spring shut (4)
I believe the answer is:
snap
'shut' is the definition.
(I know that snap is a type of shut)
'tin with a power' is the wordplay.
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'with' is a charade indicator (letters next to each other).
'power' becomes 'p'.
'sn'+'a'+'p'='SNAP'
'to spring' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for snap that I've seen before include "Click! - a photograph!" , "Still" , "Snarl at - photograph" , "Speak sharply or break suddenly" , "Break - children's card game" .)