The Collaborative International Dictionary
Luck \Luck\, n. [Akin to D. luk, geluk, G. gl["u]ck, Icel. lukka, Sw. lycka, Dan. lykke, and perh. to G. locken to entice. Cf. 3d Gleck.] That which happens to a person; an event, good or ill, affecting one's interests or happiness, and which is deemed casual; a course or series of such events regarded as occurring by chance; chance; hap; fate; fortune; often, one's habitual or characteristic fortune; as, good, bad, ill, or hard luck. Luck is often used by itself to mean good luck; as, luck is better than skill; a stroke of luck.
If thou dost play with him at any game,
Thou art sure to lose; and of that natural luck,
He beats thee 'gainst the odds.
--Shak.
Luck penny, a small sum given back for luck to one who pays money. [Prov. Eng.]
To be in luck, to receive some good, or to meet with some success, in an unexpected manner, or as the result of circumstances beyond one's control; to be fortunate.
Wiktionary
n. A small sum given back for luck to one who pays money.
Usage examples of "luck penny".
The kick-back system probably stemmed from the Irish 'luck penny': if you bought a horse from an Irishman he gave you back a penny of your money for luck.