Pronunciation: (i-rat'ik),[key] —adj. 1. deviating from the usual or proper course in conduct or opinion; eccentric; queer: erratic behavior. 2. having no certain or definite course; wandering; not fixed: erratic winds. 3. Geol.noting or pertaining to a boulder or the like carried by glacial ice and deposited some distance from its place of origin.
4. (of a lichen) having no attachment to the surface on which it grows.
—n. 1. an erratic or eccentric person.
2. Geol.an erratic boulder or the like.