Star some compulsive gambler (4)
I believe the answer is:
vega
'star' is the definition.
(Vega is an example)
'some compulsive gambler' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'VEGA' is hidden in the letters of 'compulsive gambler'.
(Other definitions for vega that I've seen before include "Brightest star of constellation Lyra" , "Bright star of constellation Lyra" , "First magnitude star" , "Fifth brightest star" , "Star in Lyra; grassy plain (Spanish)" .)