Current one working bearing string instrument (9)
I believe the answer is:
accordion
'instrument' is the definition.
(accordion is a kind of instrument)
'current one working bearing string' is the wordplay.
'current' becomes 'ac' (alternating current).
'one' becomes 'i' (Roman numeral).
'working' becomes 'on' (on can mean working or activated).
'bearing' says to put letters next to each other.
'string' becomes 'cord' (I've seen this before).
'i'+'on'='ion'
'ion' put after 'cord' is 'cordion'.
'ac'+'cordion'='ACCORDION'
(Other definitions for accordion that I've seen before include "Agreement starts the musical instrument" , "Bellows-operated instrument" , "squeeze it while operating keys" , "Squeeze box" , "It's played" .)