From The Collaborative International Dictionary of English v.0.48 :
Jackpot \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]
From WordNet (r) 3.0 (2006) :
jackpot
n 1: the cumulative amount involved in a game (such as poker)
[syn: pot, jackpot, kitty]
2: any outstanding award