unpredictable

• "an unpredictable (or indeterminable) future"

• "an irregular heartbeat"

Synonyms

• irregulara member of an irregular armed force that fights a stronger force by sabotage and harassment ; merchandise that has imperfections; contrary to rule or accepted order or general practice; not occurring at a regular rate or fixed intervals; (used of the military) not belonging to or engaged in by regular army forces; (of solids) not having clear dimensions that can be measured; failing to meet a standard of manufacture due to an imperfection; deviating from normal expectations; lacking continuity or regularity; (of a surface or shape); independent in behavior or thought