One pressed to make sound agreement with one working (9)
I believe the answer is:
accordion
'one pressed to make sound' is the definition.
I can't tell whether this definition defines the answer.
'agreement with one working' is the wordplay.
'agreement' becomes 'accord' (an accord is a formal agreement).
'with' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'working' becomes 'on' (e.g. a machine is working or on).
'accord'+'i'+'on'='ACCORDION'
Can you help me to learn more?
(Other definitions for accordion that I've seen before include "It's played" , "Agreement starts the musical instrument" , "box-shaped musical instrument like melodeon" , "Squeeze box" , "Squeeze-box" .)