Flag from fair I snatched (4)
I believe the answer is:
iris
'flag' is the definition.
('iris' can be a synonym of 'flag')
'from fair i snatched' is the wordplay.
'from' says the answer is hidden in the clue.
'IRIS' is hidden within 'fair i snatched'.
(Other definitions for iris that I've seen before include "One controlling pupil' s reactions" , "Coloured part of the lamp" , "Circular coloured membrane in the eye" , "Flag or flower in the eye" , "who keeps pupil in?" .)