ninth / nīn[unvoicedth]/ • ordinal number constituting number nine in a sequence; 9th: the ninth century | the ninth of March. ∎ (a ninth/one ninth) each of nine equal parts into which something is or may be divided. ∎ the ninth finisher or position in a race or competition: he came in ninth. ∎ the ninth and final inning of a regulation baseball game: he was rocked for five runs in the ninth. ∎ the ninth grade of a school. ∎ Mus. an interval spanning nine consecutive notes in a diatonic scale. ∎ Mus. the note that is higher by this interval than the tonic of a diatonic scale or root of a chord. ∎ Mus. a chord in which the ninth note above the root forms an important component.DERIVATIVES: ninth·ly adv.