Source : Webster's Revised Unabridged Dictionary (1913)

Octave \Oc"tave\, n. [F., fr. L. octava an eighth, fr. octavus
   eighth, fr. octo eight. See {Eight}, and cf. {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. (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.