Any larger-than-usual gambling prize formed by the accumulation of unwon bets.
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.
4.
An unusually large success in an enterprise, either unexpected or unpredictable, esp. one providing a great financial benefit.
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.
... either vanished or returned swiftly without any believable explanation of what they had seen—wanting only to get away from her as quickly as possible. But the man who could bring her in—or even strip her clean in space—that man would win the jackpot. ... — All Cats Are Gray • Andre Alice Norton
... later we was chuggin' away from the little natural jackpot that we'd opened so successful, headed for the Agnes. And, believe me, the old yacht looks mighty homey and invitin', lyin' there in the calm of the mornin' with all her awnin's spread and a trickle of blue smoke driftin' up ... — Wilt Thou Torchy • Sewell Ford
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