means The seemingly random force that decides whether good or bad things happen to you, without any effort or merit on your part.

from Borrowed in the late Middle Ages from the Low Countries — Middle Dutch 'luc', a shortened form of 'gheluc', meaning happiness or good fortune. It likely sailed into English on the back of gambling and trade, the way useful words often do, and is related to German 'Glück'. Fittingly for a word about chance, its deeper roots fade out into the unknown.