"500” race (4)
I believe the answer is:
indy
'500 race' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for indy that I've seen before include "500-mile US motorcar race" , "US car race" , "Racing in fast cars" , "US motor-racing" , "- - Car racing (in US)" .)