Ring in order for instrument (4)
I believe the answer is:
oboe
'instrument' is the definition.
(oboe is a kind of instrument)
'ring in order' is the wordplay.
'ring' becomes 'o'.
'in' is an insertion indicator.
'order' becomes 'obe'.
'o' put inside 'obe' is 'OBOE'.
'for' is the link.
(Other definitions for oboe that I've seen before include "Woodwind instrument of treble pitch" , "Orchestral piece" , "Slender double-reed instrument" , "Double-reed woodwind" , "Double-reeded woodwind instrument" .)