deviation (n.)

late 14c., "a going astray, a turning aside from the (right) way or course, a going wrong, error," from Late Latin deviatus, past participle of deviare "turn aside, turn out of the way," from Latin phrase de via, from de "off, away" (see de-) + via "way" (see via). From 1630s as "departure from a certain standard or rule of conduct or original plan." Statistical sense is from 1858; standard deviation is from 1894. Related: Deviational.