/ Dictionary / Index N ninth chord: Meaning and Definition of Find definitions for: ninth' chord" Pronunciation: [key] — Music. Music. a chord formed by the superposition of four thirds. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Ninth Amendment Ninth Commandment Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language