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.

&fist; 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.

4. A small cask of wine, the eighth part of a pipe.

Oc"tave (?), a. Consisting of eight; eight. Dryden.

• (music theory) An interval of eight tones on a scale, representing a doubling or halving in pitch.
        The melody jumps up an octave at the beginning, then later drops back down an octave.
        The singer was known for astounding clarity over her entire five-octave range.
  
• (music theory) The pitch an octave higher than a given pitch.
        The bass starts on a low E, and the tenor comes in on the octave.