Crossword Genius

Excess food storage? Fine to be ripped off (4)

Ross

I believe the answer is:

lake

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'excess' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for lake that I've seen before include "Superior maybe < that's red" , "Pool" , "Superior, e.g." , "Mere - organic pigment" , "Water in North Italy" .)

I've seen this clue in The Times and The Sunday Times.
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