noun
big gamble; risky speculation; large bet
Refers to a high-stakes gamble, whether literal betting or a risky venture with large potential loss or gain.
その投資は大博打だったが、成功した。
That investment was a big gamble, but it succeeded.
彼は大博打を打って、全財産を失った。
He made a huge bet and lost his entire fortune.
Compound of 大 (big) and 博打 (gambling). The exact historical derivation is uncertain, but the word is straightforwardly formed from these elements.