Good fortune or a happy outcome, especially by chance. For example, It was sheer good luck that brought this offer my way, or, as Shakespeare put it in The Merry Wives of Windsor (3:5): “As good luck would have it, comes in one Mistress Page.” [Late 1400s]
Also, good luck to you. I wish you success. This term is used both straightforwardly, as in Good luck on your journey, and sarcastically, implying that what someone is undertaking is not likely to succeed, as in If you think you'll find that long-lost letter, good luck to you.
Examples from the Web for good luck
Noticing the horse-shoe over the fire-place, she inquired whether it were hung there to keep off witches, or for good-luck.Mark Gildersleeve|John S. Sauzade
While I was yet foraging for my horse's supper, by good-luck in came the postmaster.Round About the Carpathians|Andrew F. Crosse
I swear I never could have passed in Latin but for your good-luck charm.The Little Colonel: Maid of Honor|Annie Fellows Johnston
The voyage commenced pleasantly, and we had the good-luck to have the ladies' cabin to ourselves.
When the sun set, and warned her that it was time to go home, she hadn't seen a thing that looked like the good-luck plant.