erratic

adjective
1
not happening at regular times; not following any plan or regular pattern; that you cannot rely on
نامنظم, غیرقابل‌پیش‌بینی, ناپایدار, بی‌ثبات, غیرقابل‌اتکا
synonym unpredictable
noun
1
a large rock that is different from the rock around it and was left behind when a large mass of ice melted
صخره سرگردان, سنگ یخچالی, سنگ سرگردان