octave

noun

• 1 Music a series of eight notes occupying the interval between (and including) two notes, one having twice or half the frequency of vibration of the other.
• the interval between the two notes at the extremes of an octave.
• each of the two notes at the extremes of an octave.
• the two notes at the extremes of an octave sounding together.

• 2a group or stanza of eight lines; an octet.

• 3the seventh day after a Church festival.
• a period of eight days beginning with the day of a Church festival.

• 4 Fencing the last of eight parrying positions.

• 5British a wine cask holding an eighth of a pipe.