[ 'ɒktɪv ]
■ 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 these two notes.
↘each of the two notes at the extremes of this interval.
↘these two notes sounding together.
2》 a group or stanza of eight lines.
3》 the seventh day after a Church festival.
↘a period of eight days beginning with the day of such a festival.
4》 Fencing the last of eight parrying positions.
5》 Brit. a wine cask holding an eighth of a pipe.
Origin
ME (in sense 3): via OFr. from L. octava dies 'eighth day'.