/ Dictionary / Index L Lyonnesse: Meaning and Definition of Find definitions for: Ly•on•nesse Pronunciation: (lī"u-nes'), [key] — n. Arthurian Romance. the mythical region where Sir Tristram was born, located near Cornwall in SW England and supposed to have been submerged by the sea. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. lyonnaise Lyon Office of Arms 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