Characterized by unpredictable or irregular behavior; inconsistent and unreliable in a way that seems random.
Derived from 'erratic' with the suffix '-al' added for emphasis or to create an adjectival form. Both ultimately trace to Latin 'erraticus' from 'errare' (to wander).
Medieval scholars used this word to describe planets that seemed to move against the normal patterns of the sky—they called them 'erratic stars,' not knowing about gravity! The word stuck around even after we understood planetary motion.
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