/ Dictionary / Index M median plane: Meaning and Definition of Find definitions for: me'dian plane' Pronunciation: [key] a vertical plane that divides an organism into symmetrical halves. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. median lethal dose median point Related Content Daily Word Quiz: clairvoyant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language