/ Dictionary / Index D decennium: Meaning and Definition of Find definitions for: de•cen•ni•um Pronunciation: (di-sen'ē-um), [key] — pl. -cen•ni•ums, -cen•ni•a a period of ten years; a decade. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: decennium (Thesaurus) decennial decent Related Content Daily Word Quiz: impetuous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language