erratic

Etymology

From Middle English erratik, erratyk, from Latin errāticus; compare Old French erratique.

adj

1. Unsteady, random; prone to unexpected changes; not consistent.
   Henry has been getting erratic scores on his tests: 40% last week, but 98% this week.
2. Deviating from normal opinions or actions; eccentric; odd.
   erratic conduct

noun

1. (geology) A rock moved from one location to another, usually by a glacier.
   The term for a displaced boulder is an erratic, but in the nineteenth century the expression seemed to apply more often to the theories than to the rocks. 2003, Bill Bryson, A Short History of Nearly Everything, BCA, page 372
   During the last ice-age, massive stones were carried for miles by the scouring glaciers, only to be left, like passengers at the end of the line, when the glaciers retreated. Stranded in their new surroundings with rocks with which they share no common geology, their out-of-place-ness is evoked by their name: “erratics”. 2015-05-04, Dominick Tyler, “10 UK landscape features that you’ve probably never heard of”, in The Guardian
2. Anything that has erratic characteristics.