Bottle is commonly used in British betting slang to describe these odds. The term dates back to the early days of horse racing, where specific odds were associated with slang terms. In this case, if you bet one unit and win, you’ll receive your initial unit back, plus two more for a total of three units. These odds are seen as relatively favorable in some contexts.
Bottle Example
For example, if a bettor places a £10 bet on a horse at bottle odds (2/1) and the horse wins, the bettor would win £20, plus the return of their original £10, for a total payout of £30.