sixth 
(sĭksth)
(sĭksth)n.
1. The ordinal number matching the number six in a series.
2. One of six equal parts.
3. Music
a. An interval of six degrees in a diatonic scale.
b. A tone separated by this interval from a given tone.
c. The harmonic combination of two tones separated by this interval.
d. The sixth tone of a scale; the submediant.
sixth adv. & adj.