sixth / siks[unvoicedth]/ • ordinal number constituting number six in a sequence; 6th: her sixth novel the sixth of the month to the original five categories we add a sixth. ∎  (a sixth/one sixth) each of six equal parts into which something is or may be divided: a sixth of the total population. ∎  the sixth finisher or position in a race or other competition: he could only finish sixth. ∎  the sixth grade of a school. ∎  sixthly (used to introduce a sixth point or reason): sixth, given all the facts there is no logical reason why we can't make a decision. ∎  Mus. an interval spanning six consecutive notes in a diatonic major or minor scale, e.g., C to A (major sixth) or A to F (minor sixth). ∎  Mus. the note that is higher by this interval than the tonic of a scale or root of a chord.DERIVATIVES: sixth·ly adv.

sixth. Interval in melody or harmony, encompassing 6 degrees of the major or minor scale, counting bottom and top notes. Major 6th is distance, for instance, from C up to A, minor 6th (semitone less) from C up to A♭, augmented 6th (semitone more) from C up to A♯. See Neapolitan 6th.