aleatory

If you're the gambling type, then chances are good you've come across aleatory in your travels. Deriving from the Latin noun alea, which refers to a kind of dice game, aleatory was first used in English in the late 17th century to describe things that are dependent on uncertain odds, much like a roll of the dice. The term now describes things that occur by sheer chance or accident, such as the unlucky bounce of a golf shot or the unusual shape of an ink blot. Going a bit further, the term "aleatory music" (also called "aleatoric music" or "chance music") describes a musical composition in which certain parts are left for the performer to concoct through improvisation.