the.com/bookmaker

means A person who professionally sets odds and takes bets on the outcomes of events, especially horse racing and sports.

from A straightforward trade name from the 19th century: someone who 'makes a book' — literally kept a ledger recording all the bets placed on a race, with their amounts and odds, so the wagers could be tracked and paid out. 'Book' here means account-book, not a bound novel. The trade grew up alongside organized horse racing in Britain, where odds-setting became formalized enough to need a dedicated record-keeper — who, cannily, set the odds in his own favor.