decennium definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
decennium definition by American Heritage Dictionary
noun pl. de·cen·ni·ums or de·cen·ni·a
A period of ten years; a decade.
Origin: Latin, from decennis, lasting for ten years : decem, ten; see dekm̥ in Indo-European roots + annus, year; see at- in Indo-European roots.