Crossword Genius

Reportedly, not the whole amount (3)

Ross

I believe the answer is:

sum

I'm a little stuck... Click here to teach me more about this clue!

'whole amount' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for sum that I've seen before include "Amount of money; total" , "Amount, of money say" , "maths problem" , "pupils find it a problem" , "All one has" .)

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