Definition of: octave

(ok′tiv, -tāv) noun
1. Music a The interval between any note and that given by twice as many or by half as many vibrations in a second. b A note at this interval above or below any other, considered in relation to that other. c Two notes at this interval, sounded together; also, the resulting consonance. d An organ stop giving tones an octave higher than those normally corresponding to the keys played.
2. The eighth day from a feast day, beginning with the feast day as one; also, the lengthening of a festival so as to include a period of eight days.
3. Any group or series of eight.
4. In prosody, the first eight lines in an Italian sonnet, or a stanza of eight lines.
—adjective
1. Composed of eight.
2. In prosody, composed of eight lines.
3. Music Producing tones an octave higher. Also oc·ta·val (ok·tā′vəl, ok′tə-) adjective [<OF <L octava, fem. of octavus eighth <octo eight]