Ninth
An interval one degree beyond the octave, being the second removed an octave; it may, like the second, be minor, major, or augmented. The minor and major ninths are essential dissonances, that is, sounds derived from the fundamental; with the augmented ninth the lower sound is really the ninth, thus, G, B, D, F, A or Ab, are overtones of G, but C, D arise from B, D, F#, A, C, chord of ninth. A chord consisting of root major 3, per. 5, minor 7, and major or minor ninth may have either major or minor ninth in major keys, but only the minor ninth in minor keys.