Silver revolver initially carried by spy (6)
I believe the answer is:
argent
'silver' is the definition.
('argent' can be a synonym of 'silver')
'revolver initially carried by spy' is the wordplay.
'revolver initially' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'carried by' means one lot of letters goes inside another.
'spy' becomes 'agent' (I've seen this before).
'r' going inside 'agent' is 'ARGENT'.
Can you help me to learn more?
(Other definitions for argent that I've seen before include "Tincture of silver in heraldry" , "Colour" , "(In heraldry) silver - garnet (anag)" , "Heraldic silver in garnet" , "Silver in 1 Down" .)