Proof impudence repelled you once (6)
I believe the answer is:
galley
'proof' is the definition.
(galley proof is a kind of proof)
'impudence repelled you once' is the wordplay.
'impudence' becomes 'gall' (synonyms).
'repelled' is a reversal indicator.
'you once' becomes 'ye' (historical version of 'you').
'ye' in reverse letter order is 'ey'.
'gall'+'ey'='GALLEY'
(Other definitions for galley that I've seen before include "Cookhouse on board" , "Kitchen on board" , "Kitchen aboard ship" , "Vessel's kitchen" , "Trireme" .)