late 14c., "change, transformation, action of altering," from Old French alteracion "change, alteration" (14c.), and directly from Medieval Latin alterationem (nominative alteratio), noun of action from past-participle stem of Late Latin alterare "to change," from Latin alter "the other (of the two)," from PIE root *al- (1) "beyond" + comparative suffix -ter (as in other). Meaning "change in character or appearance" is from 1530s; that of "change in ready-made clothes to suit a customer's specifications" is from 1901. Related: Alterations.
