Did Polish brand start to invent junk? (9)
I believe the answer is:
burnished
'did polish' is the definition.
('burnish' can be a synonym of 'polish')
'brand start to invent junk?' is the wordplay.
'brand' becomes 'burn' (brand can mean to burn a mark into something).
'start to' suggests taking the first letters.
'junk?' becomes 'shed' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'invent' is 'i'.
'burn'+'i'+'shed'='BURNISHED'
Can you help me to learn more?
(Other definitions for burnished that I've seen before include "shone" , "made lustrous" .)