Green’s Dictionary of Slang

(orig. US) a piece of good luck.

1973–77		J. Jones Whistle 547: But this did not stop the cook from bragging about what a luckout and great night the two of them had had [HDAS].
1997–99		vronsky & westerman Randgold 🌐 ‘Morila has been a luck out for us,’ Kebble proclaims. The economics do appear fantastic, with an expected payback of 15 months.