Supermarket said to be getting bigger (6)

I believe the answer is:

grocer

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'supermarket' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for grocer that I've seen before include "Market trader" , "Retail merchant" , "Dealer in foodstuffs and household goods" , "Provisions purveyor" , "Seller of food and household supplies" .)

I've seen this clue in The Globe and Mail.

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