Honours involving old members of an orchestra? (5)
I believe the answer is:
oboes
'members of an orchestra?' is the definition.
(oboes are orchestral instruments)
'honours involving old' is the wordplay.
'honours' becomes 'OBEs' (Order of the British Empire awards).
'involving' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'obes' placed around 'o' is 'OBOES'.
(Other definitions for oboes that I've seen before include "Parts of orchestra" , "They're instrumental" , "members of orchestra" , "Woodwind instruments" , "Reed instruments" .)