EXAMPLES FROM THE WEB FOR BETTOR
But a bettor of the right sort slips in an' taps me for odds to a thousand.
The action was scarcely performed, when the bettor flung the glove into the air with all his force.
The bettor's friends at once began sympathizing with him, but he looked at Terry and asked if he considered that a good shot.
I was taking the same losing risk as the bettor, with a greater chance for gain.
Frequently the bettor may realize that he has won a point, or two, or three, and may insist upon the bucket shop selling for him.
It is no ordinary gamble, for what the bettor stakes is his life, possibly his reason.
also better (OED notes that English agent nouns in -er tend to shift toward -or as their senses become more specific), agent noun from bet (v.).