Sharp chance? (10)

I believe the answer is:

accidental

I believe this clue is a double definition.

'sharp' is the first definition.
(in music, sharps and flats are accidentals)

'chance?' is the second definition.
('accidental' can be a synonym of 'chance')

(Other definitions for accidental that I've seen before include "Unintended - sort of note" , "Chance, inadvertent" , "not intended by composer?" , "Casual" , "change of key" .)

I've seen this clue in The Times.

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