Girl in middle is some looker! (4)
I believe the answer is:
iris
'some looker' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'girl in middle is' is the wordplay.
'in middle' indicates the central letters.
The middle letters of 'girl' are 'ir'.
'ir'+'is'='IRIS'
Can you help me to learn more?
(Other definitions for iris that I've seen before include "Coloured eye part" , "Fleur-de-lis" , "Rainbow-goddess" , "Pupil is at the centre of this" , "Bright flower or eye part" .)