Greek god's head set in a ring (6)
I believe the answer is:
apollo
'greek god's' is the definition.
(Apollo is an example)
'head set in a ring' is the wordplay.
'head' becomes 'poll' (poll is a now rare word for head or scalp**).
'set in' indicates putting letters inside.
'ring' becomes 'o'.
'a'+'o'='ao'
'poll' going inside 'ao' is 'APOLLO'.
(Other definitions for apollo that I've seen before include "Japanese dish" , "US space program" , "handsome youth" , "mission of high-flying Americans?" , "Greek god of light, poetry, music, healing and prophecy" .)