Ninth

Simply, where ninth chords such as F9 require the inclusion of the dominant seventh, chords such as F add9 should not have the seventh.

Hence, the notes in F add9 are F A C G, and the notes in Fm add9 are F Ab C G.

Ninth (?), a. [From Nine; cf. AS. nigo&edh;a.]

1.

Following the eight and preceding the tenth; coming after eight others.

2.

Constituting or being one of nine equal parts into which anything is divided.

© Webster 1913.

Ninth, n.

1.

The quotient of one divided by nine; one of nine equal parts of a thing; the next after the eighth.

2. Mus. (a)

An interval containing an octave and a second.

A chord of the dominant seventh with the ninth added.

© Webster 1913.