Crossword Genius

On the radio, shopkeeper is more boorish (7)

Ross

I believe the answer is:

grosser

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'more boorish' is the definition.
Both the answer and definition are comparative adjectives. Perhaps you can see an association between them that I don't see?

'on the radio shopkeeper' is the wordplay.
'on the radio' shows a homophone (sound like).
'shopkeeper' becomes 'grocer' (I've seen this before).
'grocer' is a homophone of 'GROSSER'.

'is' is the link.

Can you help me to learn more?

(Other definitions for grosser that I've seen before include "more vulgar" , "More corpulent" .)

I've seen this clue in The Independent.
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