Purple flower (5)
(Other definitions for aster that I've seen before include "Stare (anag.)" , "Plant like a Michaelmas daisy" , "Showy garden flower" , "Flower of the daisy family - rates (anag)" , "Stare at pretty flower" .)
'purple flower' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for iris that I've seen before include "Coloured eye part" , "Pupil is at the centre of this" , "who keeps pupil in?" , "Flowers in the eye?" , "bloomer?" .)