aleatory

(āˈlē-ə-tôrˌē, -tōrˌē)

1. Dependent on chance, luck, or an uncertain outcome: an aleatory contract between an oil prospector and a landowner.
2. Of or characterized by gambling: aleatory contests.
3. also a·le·a·to·ric (āˌlē-ə-tôrˈĭk, -tōrˈ-) Music Using or consisting of sounds to be chosen by the performer or left to chance; indeterminate: An object placed inside the piano added an aleatory element to the piece.