*jackpot*

n. 1. Same as jack pot. See under jack. [ PJC ]

2. Any larger-than-usual gambling prize formed by the accumulation of unwon bets. [ PJC ]

3. The highest gambling prize awarded in a gambling game in which smaller prizes are also awarded, especially such a prize on a slot machine. [ PJC ]

4. An unusually large success in an enterprise, either unexpected or unpredictable, esp. one providing a great financial benefit. [ PJC ]

hit the jackpot to receive an unexpectedly large (or the largest possible) benefit from an enterprise; as, after prospecting for years, he finally hit the jackpot when he discovered a silver lode. [ PJC ]