Aleatory

aleatory \ˈā-lē-ə-ˌtor-ē\ adjective: 1: depending on an uncertain event or contingency as to both profit and loss {an aleatory contract}, 2: relating to luck and especially to bad luck, 3: aleatoric; characterized by chance or indeterminate elements {aleatory music}

Etymology: Latin aleatorius of a gambler, from aleator gambler, from alea a dice game

I first heard this term as a descriptor of certain 20th century music.