Kit one used in a piano piece (American) (9)

I believe the answer is:

apparatus

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'kit one' is the definition.
'apparatus' can be an answer for 'kit' (thesaurus). I'm not sure about the 'one' bit.

'a piano piece american' is the wordplay.
'a piano piece' becomes 'apparat' (I can't explain this - if you can you should give a lot more credence to this answer).
'american' becomes 'us'.
'apparat'+'us'='APPARATUS'

'used in' is the link.

Can you help me to learn more?

(Other definitions for apparatus that I've seen before include "system" , "Equipment, device" , "Equipment, gear" , "Set of equipment serving a specific purpose" , "Collection of equipment designed for a particular purpose" .)

I've seen this clue in The Independent.

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