Pari

un pari = a bet, a wager. From the verb parier = to bet.

E.g.:
le pari de Pascal = Pascal's wager (philosopher and mathematician Blaise Pascal's probablilistic justification for belief in God)
pari tenu! = you're on!
je te tiens le pari que... = I bet you that...
tu paries ? = you want to bet ?
il a parié gros sur un cheval, et il a perdu = he bet heavily on a horse, and he lost