stochastic

The adjective stochastic describes something that has a random variable. You like to joke that the city buses follow a stochastic schedule because they arrive at random times at the various bus stops.

Stochastic is from the Greek word stokhastikos, meaning able to guess, with the root stokhos meaning a target––in Greek stokhos literally means a stick meant for archers to shoot at. The "guess" part of the original Greek work is still part of the word's meaning today: A stochastic process in a computer program, for example, is one where you can't predict what is going to happen in the program because of something random in it.