/ Dictionary / Index D diencephalon: Meaning and Definition of Find definitions for: di•en•ceph•a•lon Pronunciation: (dī"en-sef'u-lon"), [key] — pl. -lons, -la the posterior section of the forebrain. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: diencephalon (Thesaurus) Dien Bien Phu diene Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language