One clicks what St Peter might have done (8)
I believe the answer is:
castanet
'peter might have done' is the definition.
I can't judge whether this definition defines the answer.
'one clicks what st' is the wordplay.
I cannot really see how this works, but
'one' could be 'ane' (synonyms) and 'ane' is found within the answer.
'st' is found in the answer.
The remaining letters 'cat' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for castanet that I've seen before include "Single Spanish percussion" , "Scant tea (anag.)" , "One of a pair in Spanish music" , "something resembling a shell" , "Spanish clicker" .)