Other forms: wagers; wagered; wagering
To wager is to bet: you might say to your fellow train passengers, "I'll wager ten dollars that we won't get to Chicago on time."
You can use the word wager as either a noun or a verb, to mean "place a bet" or "the amount of money being risked in a bet." So you could offer a wager at the poker table, or ask if anyone wants to wager on Monday's football game. Either way you use it, wager is a Middle English word that comes from the Old North French wage, "to pledge."