Crossword Genius

Plump sumo wrestler eats a significant amount (4,3)

Ross

I believe the answer is:

lump sum

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'a significant amount' is the definition.
The definition suggests a singular noun which matches the answer.

'plump sumo wrestler eats' is the wordplay.
'LUMP SUM' is hidden within the letters.
However, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for lump sum that I've seen before include "Single cash payment" , "Single payment as opposed to a number of smaller ones" , "Whole payment" , "one lot of money" , "Single payment as opposed to many instalments" .)

I've seen this clue in The Irish Times.
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