IPA: //ˈbɛtər//
KK: /ˈbɛtər/
A person who places a wager or gamble on the outcome of an event, often in games or sports.
The bettor placed a large bet on the horse race.
Bettor → The word is formed from 'bet' (from Old English 'bet', meaning to stake or wager) and the suffix '-or' (meaning one who). A bettor is one who stakes or wagers on an outcome.
Think of someone who 'stakes' something on a chance — that's what a bettor does.