Oscar after Henry's ring (4)
I believe the answer is:
halo
'ring' is the definition.
(I've seen this before)
'oscar after henry's' is the wordplay.
'oscar' becomes 'o' (phonetic alphabet: alpha, bravo, charlie etc.).
'after' means one lot of letters go next to another.
'henry' becomes 'hal'.
'o' put after 'hal' is 'HALO'.
(Other definitions for halo that I've seen before include "Luminous ring" , "Saint's overhead ring of light" , "Glittering aura" , "Hagiological aura featured in Christian art" , "that could make one light-headed?" .)