One better (7)
I believe the answer is:
gambler
This clue could be a double definition.
'one' is the first definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'better' is the second definition.
(a gambler is someone who bets)
Can you help me to learn more?
(Other definitions for gambler that I've seen before include "One who bets" , "Speculator" , "One who takes risks" , "Better" , "Risk-taker" .)