Honour holding old musical instrument (4)
I believe the answer is:
oboe
'musical instrument' is the definition.
(oboe is a kind of musical instrument)
'honour holding old' is the wordplay.
'honour' becomes 'obe'.
'holding' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'obe' placed around 'o' is 'OBOE'.
(Other definitions for oboe that I've seen before include "Cor anglais in its family" , "Walk with exaggerated movements" , "bit of wind" , "Producer of notes" , "it's blown" .)