uncertain ambiguous (especially in the negative); "she spoke in no uncertain terms"
aleatory dependent on chance; "the aleatory element in life"
capricious,
freakish determined by chance or impulse or whim rather than by necessity or reason; "a capricious refusal"; "authoritarian rulers are frequently capricious"; "the victim of whimsical persecutions"
episodic,
occasional limited in duration to a single episode; "an account concerned primarily with episodic events such as the succession of rulers"
unpredictable -
unknown in advance; "an unpredictable (or indeterminable) future"
