Aleatory means "pertaining to luck", and derives from the Latin word alea, the rolling of dice. Aleatoric, indeterminate, or chance art is that which exploits the principle of randomness.
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[adj] dependent on chance; "the aleatory element in life"
unpredictable
absolute music, accidental, adaptation, adventitious, adventurous, air varie, aleatoric, aleatory music, amorphous, arrangement, blobby, blurred, blurry, broad, casual, causeless, chamber music, chamber orchestra, chance, chancy, chaotic, circumstantial,
\A"le*a*to*ry\, a. [L. aleatorius, fr. alea chance, die.] (Law) Depending on some uncertain contingency; as, an aleatory contract. --Bouvier.