Iodine in lead instrument (5)
I believe the answer is:
sitar
'instrument' is the definition.
(sitar is a kind of instrument)
'iodine in lead' is the wordplay.
'iodine' becomes 'i' ('I' can be a synonym of 'iodine').
'in' is an insertion indicator.
'lead' becomes 'star' (I've seen this before).
'i' placed inside 'star' is 'SITAR'.
(Other definitions for sitar that I've seen before include "Large Indian lute" , "Guitar-like instrument" , "Indian string instrument" , "Long necked and often plucked" , "Long-necked musical instrument of India" .)