aleatory

UK: /ˈeɪlɪətərɪ/ US: (ā′lē ə tôr′ē, -tōr′ē, al′ē-)

WordReference Random House Unabridged Dictionary of American English © 2025

a•le•a•to•ry  (ā′lē ə tôr′ē, -tōr′ē, al′ē-), adj. 

1. Law depending on a contingent event:
   an aleatory contract.
2. of or pertaining to accidental causes; of luck or chance;
   unpredictable:
   an aleatory element.
3. Music, Music and Dance employing the element of chance in the choice of tones, rests, durations, rhythms, dynamics, etc.

Also, a•le•a•tor•ic  (ā′lē ə tôr′ik, -tor′-, al′ē-). 

• Latin āleātōrius, equivalent. to āleātōr- (stem of āleātor gambler (āle(a) game of chance + -ātor -ator) + -ius adjective, adjectival suffix; see -tory¹
• 1685–95

Collins Concise English Dictionary © HarperCollins Publishers::

aleatory / ˈeɪlɪətərɪ -trɪ/, aleatoric / ˌeɪlɪəˈtɒrɪk/ adjective

1. dependent on chance
2. (esp of a musical composition) involving elements chosen at random by the performer

Etymology: 17th Century: from Latin āleātōrius, from āleātor gambler, from ālea game of chance, dice, of uncertain origin