Oc·tave n.
  1. The eighth day after a church festival, the festival day being included; also, the week following a church festival. “The octaves of Easter.”
  2. Mus. (a) 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) The whole diatonic scale itself.
  Note: ☞ 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.
  Double octave. Mus. See under Double.
  Octave flute Mus., 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.