See decennium in American Heritage Dictionary 4
noun pl. de·cen·ni·ums or de·cen·ni·a (-sĕnˈē-ə)
Origin:
Origin: Latin
Origin: , from decennis, lasting for ten years
Origin: : decem, ten; see dekm̥ in Indo-European roots
Origin: + annus, year; see at- in Indo-European roots
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