octave

1. An interval of twelve semitones spanning eight degrees of the diatonic scale, representing a doubling or halving in pitch frequency.

   The melody jumps up an octave at the beginning, then later drops back down an octave.

2. The pitch an octave higher than a given pitch.

   The bass starts on a low E, and the tenor comes in on the octave.

3. A coupler on an organ which allows the organist to sound the note an octave above the note of the key pressed (cf sub-octave)
4. A poetic stanza consisting of eight lines; usually used as one part of a sonnet.
5. The eighth defensive position, with the sword hand held at waist height, and the tip of the sword out straight at knee level.
6. The day that is one week after a feast day in the Latin rite of the Catholic Church.
7. An eight-day period beginning on a feast day in the Latin rite of the Catholic Church.
8. An octonion.
9. Any of a number of coherent-noise functions of differing frequency that are added together to form Perlin noise.
10. The subjective vibration of a planet.

adjective

Consisting of eight; eight in number.