deviating from the usual or proper course in conduct or opinion; eccentric; queer

erratic behavior.

having no certain or definite course; wandering; not fixed

erratic winds.

Geology . noting or pertaining to a boulder or the like carried by glacial ice and deposited some distance from its place of origin.

(of a lichen) having no attachment to the surface on which it grows.

an erratic or eccentric person.

Geology . an erratic boulder or the like.