Top bets are lost (4)
I believe the answer is:
best
'top' is the definition.
(associated in meaning)
'bets are lost' is the wordplay.
'are lost' is an anagram indicator.
'bets' anagrammed gives 'BEST'.
(Other definitions for best that I've seen before include "Cream of the crop" , "Top, finest" , "Most advantageous" , "Beat" , "Superlative" .)