noun

1. 1. the eighth day following a church festival, counting the festival day as the first
   2. the entire period between the festival and this day
2. a group of eight lines of verse; specif., the first eight lines of a Petrarchan sonnet
3. any group of eight
4. Fencing a position of thrust or parry in which the hand is rotated with the palm up
5. Music
   1. the eighth tone of an ascending or descending diatonic scale, or a tone seven degrees above or below a given tone in such a scale
   2. the interval of seven diatonic degrees between a tone and either of its octaves
   3. the series of tones contained within this interval, or the keys of an instrument producing such a series
   4. a tone and either of its octaves sounded together
   5. an organ stop producing tones an octave above those ordinarily produced by the keys struck

Etymology: OFr < L octava, fem. of octavus, eighth < octo, eight

adjective

1. consisting of eight, or an octave
2. Music producing tones an octave higher an octave key