Examples from the Web for bettor
But a bettor of the right sort slips in an' taps me for odds to a thousand.Thoroughbreds|W. A. Fraser
The action was scarcely performed, when the bettor flung the glove into the air with all his force.The Confessions of Harry Lorrequer, Complete|Charles James Lever (1806-1872)
I was taking the same losing risk as the bettor, with a greater chance for gain.My Adventures with Your Money|George Graham Rice
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.Twenty Years a Detective in the Wickedest City in the World|Clifton R. Wooldridge
It is no ordinary gamble, for what the bettor stakes is his life, possibly his reason.The Door Through Space|Marion Zimmer Bradley
Word Origin and History for bettor
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.).