From Greek stokhastikos 'able to guess,' from stokhos 'target'—an archer's skill in aiming repurposed for probability theory.
Randomly determined; having a pattern that can be analyzed statistically but not predicted precisely.
From Greek stokhastikos 'able to guess, conjecturing,' from stokhazesthai 'to aim at, guess,' from stokhos 'aim, target, guess.' The original meaning was 'skillful in aiming'—a good archer who could guess where to shoot. Jakob Bernoulli applied it to probability theory in the 17th century, and the modern mathematical sense was fixed by the 1930s.