Crossword Genius

Love what fallen hero becomes, they say (4)

Ross

I believe the answer is:

zero

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'love' is the definition.
(love is zero in tennis)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for zero that I've seen before include "Absolutely nothing" , "Nothing; freezing point (in degrees centigrade)" , "Nowt" , "Ineffective person" , "Nothing - Japanese aircraft" .)

I've seen this clue in The Guardian.
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