Webster's Revised Unabridged Dictionary · 1913

Octave

Octave , noun

[French, from Latin octava an eighth, from octavus eighth, from octo eight. See Eight, and compare Octavo, Utas.]

1.
The eighth day after a church festival, the festival day being included; also, the week following a church festival.
The octaves of Easter. — Jer. Taylor
2.
(a) (Music) The eighth tone in the scale; the interval between one and eight of the scale, or any interval of equal length; an interval of five tones and two semitones.
(b)
(Music) The whole diatonic scale itself.

The ratio of a musical tone to its octave above is 1:2 as regards the number of vibrations producing the tones.

3.
(Poet.) The first two stanzas of a sonnet, consisting of four verses each; a stanza of eight lines.
With mournful melody it continued this octave. — Sir P. Sidney
Collocations (2)
Double octave (Music) , See under Double.
Octave flute (Music) , a small flute, the tones of which range an octave higher than those of the German or ordinary flute; -- called also piccolo. See Piccolo.
4.
A small cask of wine, the eighth part of a pipe.

Octave , adjective

Consisting of eight; eight. — Dryden