From the second edition (1989):
(eɪliːəˈtɔərɪk) [f. L. āleātōr-ius (see aleatory a.) + -ic.]
Dependent on uncertain contingencies; done at random.
1961 Times 28 July 13/5 Indeterminate, or aleatoric music. 1962 Publishers' Weekly 12 Mar. 19 A new art form, known as ‘aleatoric’, meaning subject to elements of chance, is making headway among the younger generation of poets in Europe. Its leading exponent‥Maxwell Volker‥creates poetry by cutting out single words or long strips from newspapers and magazines which he haphazardly pastes together to create aleatoric verse.