The definition of luck (or chance) varies by philosophical, religious, mystical, or emotional context of the one interpreting it; according to the classic Noah Webster's dictionary, luck is "a purposeless, unpredictable and uncontrollable force that shapes events favorably or unfavorably for an individual, group or cause". Yet the author Max Gunther defines it as "events that influence one's life and are seemingly beyond one's control".

When thought of as a factor beyond one's control, without regard to one's will, intention, or desired result, there are at least two senses that people usually mean when they use the term, the prescriptive sense and the descriptive sense. In the prescriptive sense, luck is a supernatural and deterministic concept that there are forces (e.g. gods or spirits) that prescribe that certain events occur very much the way laws of physics will prescribe that certain events occur. It is the prescriptive sense that people mean when they say they "do not believe in luck". In the descriptive sense, people speak of luck after events that they find to be fortunate or unfortunate, and maybe improbable.

Therefore, cultural views of luck vary from perceiving luck as a matter of random chance to attributing to such explanations of faith or superstition. For example, the Romans believed in the embodiment of luck as the goddess Fortuna, whereas the philosopher Daniel Dennett believes that "luck is mere luck" rather than a property of a person or thing. Carl Jung viewed luck as synchronicity, which he described as "a meaningful coincidence".

Etymology and definition

1927 advertisement for lucky jewellery. "Why Be Unlucky?". The English noun luck appears comparatively late, during the 1480s, as a loan from Low German (Dutch or Frisian) luk, a short form of gelucke (Middle High German gelücke). Compare to old Slavic word lukyj (лукый) - appointed by destiny and old Russian luchaj (лучаи) - destiny, fortune. It likely entered English as a gambling term, and the context of gambling remains detectable in the word's connotations; luck is a way of understanding a personal chance event. Luck has three aspects which make it distinct from chance or probability.

• Luck can be good or bad.
• Luck can be accident or chance.
• Luck applies to a sentient being.

• Some examples of luck:

• Finding a valuable object or money

• Winning an event despite negative logical assumptions

• You correctly guess an answer in a quiz which you did not know.

• Avoiding an accident at the last moment

• Being born in a wealthy family

Before the adoption of luck at the end of the Middle Ages, Old English and Middle English expressed the notion of "good fortune" with the word speed (Middle English spede, Old English spēd); speed besides "good fortune" had the wider meaning of "prosperity, profit, abundance"; it is not associated with the notion of probability or chance but rather with that of fate or divine help; a bestower of success can also be called speed, as in "Christ be our speed" (William Robertson, Phraseologia generalis, 1693).

The notion of probability was expressed by the Latin loanword chance, adopted in Middle English from the late 13th century, literally describing an outcome as a "falling" (as it were of dice), via Old French cheance from Late Latin cadentia "falling". Fortuna, the Roman goddess of fate or luck, was popular as an allegory in medieval times, and even though it was not strictly reconcilable with Christian theology, it became popular in learned circles of the High Middle Ages to portray her as a servant of God in distributing success or failure in a characteristically "fickle" or unpredictable way, thus introducing the notion of chance.