Sign of saintliness (4)
I believe the answer is:
halo
'sign of saintliness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for halo that I've seen before include "Saint's circle of light" , "Circle over saint's head in painting" , "Aureole" , "Glittering aura" , "Nimbus" .)