Saintly circle (4)
I believe the answer is:
halo
'saintly circle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for halo that I've seen before include "Aureole" , "This indicates holiness" , "Aura round admired person" , "Sign of sainthood" , "that could make one light-headed?" .)