Saintly symbol (4)
I believe the answer is:
halo
'saintly symbol' 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 "Glowing ring (around saint's head)" , "Disc of light" , "Aura round admired person" , "Imaginary circle over saint's head" , "Luminous ring" .)