Improved as a gambler (6)
I believe the answer is:
better
This clue is a double definition.
'improved' is the first definition.
(similar in meaning)
'a gambler' is the second definition.
(someone who makes bets is a gambler)
'as' is the link.
(Other definitions for better that I've seen before include "punter" , "no longer sick" , "Partly or fully recovered from illness" , "Not as bad" , "One may lay" .)