Crossword Genius

Not quite a colleen? (4)

Ross

I believe the answer is:

iris

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'colleen?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for iris that I've seen before include "Garden flower - part of eye" , "bloomer?" , "Pupil's place?" , "Pupil is at the centre of this" , "Flag - part of eye" .)

I've seen this clue in the Evening Standard.
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