Crossword Genius

Having lost one, you can't erase the fact (6)

Ross

I believe the answer is:

rubber

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

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for rubber that I've seen before include "It can remove so-called lead" , "tough polymeric material?" , "Boring, obsessive type" , "Stretchy substance" , "item in 27 [BRIDGE]?" .)

I've seen this clue in the Evening Standard.
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