It’s played quietly (5)

I believe the answer is:

piano

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'quietly' is the definition.
('piano' can be a synonym of 'quietly')

I don't understand how the rest of the clue works.

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(Other definitions for piano that I've seen before include "Keyboard instrument" , "Musical instrument - play quietly" , "Softly (mus.)" , "entertain with this softly" , "key holder" .)

I've seen this clue in the Evening Standard.

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