Ring Henry put on Oscar (4)
I believe the answer is:
halo
'ring' is the definition.
(synonyms)
'henry put on oscar' is the wordplay.
'henry' becomes 'hal' (short for Henry).
'put on' is a charade indicator (letters next to each other).
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'hal'+'o'='HALO'
(Other definitions for halo that I've seen before include "Saint's circle of light" , "Symbol of sainthood" , "Corona" , "This indicates holiness" , "Circle over a saint" .)