Bright exterior for a chopper (7)
I believe the answer is:
cleaver
'a chopper' is the definition.
(a cleaver chops things)
'bright exterior for' is the wordplay.
'bright' becomes 'clever' (bright can mean clever or intelligent).
'exterior' means one lot of letters goes inside another (some letters go on the outside of others).
'for' becomes 'a' (I can't justify this - if you can you should give a lot more credence to this answer).
'clever' enclosing 'a' is 'CLEAVER'.
Can you help me to learn more?
(Other definitions for cleaver that I've seen before include "dangerous object?" , "Long-bladed hatchet" , "Hatchet for chopping meat" , "A clever sort of axe" , "A butcher's chopping tool" .)