/ Dictionary / Index G gnathic index: Meaning and Definition of Find definitions for: gnath'ic in'dex Pronunciation: [key] the ratio of the distance from basion to prosthion to the distance from basion to nasion, expressed in percent of the latter. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. gnathic gnathion Related Content Daily Word Quiz: supercilious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language