Definition of "luck-penny" [luck-penny]

• A small sum given back “for luck” to the purchaser or payer by the person who receives money in a bargain or other transaction. (noun)
• A copper tossed overboard “for luck.” (noun)

The Century Dictionary (Public Domain)

• "And he was baith civil and just in his dealings; and if he thought his chapman had made a hard bargain, he wad gie him a luck-penny to the mends."
• "The horse soon found a purchaser, and while the two were inside drinking the luck-penny the wizard came along and saw the horse."
• "After a bad October Tryst, where my father had sixteen score of Aberdeenshire cattle, and when he lost £4 a-head upon every beast, Mr Geddes returned him £70 as a luck-penny upon a large lot he had bought from him."