Eye part that contracts (4)
I believe the answer is:
iris
'eye part that contracts' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iris that I've seen before include "Flag - surrounding pupil" , "Goddess of the rainbow in the eye" , "Eye diaphragm" , "Bright flower or eye part" , "Rainbow-goddess" .)