Nearly being in harmony squeezing old instrument (9)
I believe the answer is:
accordion
'instrument' is the definition.
(accordion is a kind of instrument)
'nearly being in harmony squeezing old' is the wordplay.
'nearly' means to remove the last letter.
'being in harmony' becomes 'according'.
'squeezing' is an insertion indicator (squeeze can mean hug or embrace).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'according' with its last letter taken off is 'accordin'.
'accordin' placed around 'o' is 'ACCORDION'.
(Other definitions for accordion that I've seen before include "Squeeze-box" , "Agreement starts the musical instrument" , "It's played" , "Squeeze box" , "Cad I croon about a musical instrument" .)