Rossini composed, cutting son playing organ part (4)
I believe the answer is:
iris
'part' is the definition.
(iris is a kind of part)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for iris that I've seen before include "Pupil's place?" , "Murdoch in writing" , "pupil's governor" , "Nice flower or eye part" , "Lily" .)