Crossword Genius

Agreement on including one instrument (9)

Ross

I believe the answer is:

accordion

'instrument' is the definition.
(accordion is a kind of instrument)

'agreement on including one' is the wordplay.
'agreement' becomes 'accord' ('accord' can be a synonym of 'agreement'**).
'including' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'accord'+'on'='accordon'
'accordon' enclosing 'i' is 'ACCORDION'.

(Other definitions for accordion that I've seen before include "Squeeze-box" , "Cad I croon about a musical instrument" , "Agreement starts the musical instrument" , "It's played" , "Squeeze box" .)

I've seen this clue in The Times.
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