Cut Hibernian flag (4)
I believe the answer is:
iris
'flag' is the definition.
('iris' can be a synonym of 'flag')
'cut hibernian' is the wordplay.
'cut' means to remove the last letter.
'hibernian' becomes 'irish' (I've seen this before).
'irish' with its last letter taken off is 'IRIS'.
(Other definitions for iris that I've seen before include "Greek goddess of the rainbow" , "Goddess of the rainbow in the eye" , "Pupil is at the centre of this" , "Fleur-de-lis" , "Female" .)