On the radio, dealer is wine supplier (6)
I believe the answer is:
cellar
'wine supplier' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'on the radio dealer' is the wordplay.
'on' is an insertion indicator (as in clothing 'on' a person).
'the radio' becomes 'ell' (I can't explain this - if you can you should give a lot more credence to this answer).
'dealer' becomes 'car dealer' (car dealer is a kind of dealer).
'ell' placed inside 'car' is 'CELLAR'.
'is' is the link.
Can you help me to learn more?
(Other definitions for cellar that I've seen before include "Room where wine is usually stored" , "Underground storeroom" , "Wine stock; sounds like vendor" , "Wine vault" , "Room below ground for storage" .)