Hit boss with iodine, stopping ache (9)
I believe the answer is:
humdinger
'hit' is the definition.
(both can mean something successful)
'boss with iodine stopping ache' is the wordplay.
'boss with' becomes 'md' (short for managing director. I am not sure about the 'with' bit.).
'iodine' becomes 'I' (chemical symbol).
'stopping' is an insertion indicator (stopping can mean blocking a gap).
'ache' becomes 'hunger' (hungering is a kind of aching).
'md'+'i'='mdi'
'mdi' inserted inside 'hunger' is 'HUMDINGER'.
(Other definitions for humdinger that I've seen before include "Excellent person or thing (colloq)" , "something else" , "Peach" , "knockout" , "cracker" .)