n.1 Mus. a 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. b this interval. c each of the two notes at the extremes of this interval. d these two notes sounding together.
2 a group or stanza of eight lines; an octet.
3 a the seventh day after a festival. b a period of eight days including a festival and its octave.
4 a group of eight.
5 the last of eight parrying positions in fencing.
6 Brit. a wine-cask holding an eighth of a pipe.
Etymology: ME f. OF f. L octava dies eighth day (reckoned inclusively)