Extra clerical vestment picked up (7)
I believe the answer is:
surplus
'extra' is the definition.
(synonyms)
'clerical vestment picked up' is the wordplay.
'clerical vestment' becomes 'surplice' (garment worn by members of the clergy).
'picked up' indicates a 'sounds like' (homophone) clue.
'surplice' is a homophone of 'SURPLUS'.
(Other definitions for surplus that I've seen before include "Surfeit" , "Unneeded extra" , "Extra to requirements" , "(An) oversupply" , "Remainder" .)