An octave is a series of eight notes in a musical scale. It is also used to talk about the difference in pitch between the first and last notes in a musical scale.
octave in British English
(ˈɒktɪv)
noun
1.
a.
the interval between two musical notes one of which has twice the pitch of the other and lies eight notes away from it counting inclusively along the diatonic scale
b.
one of these two notes, esp the one of higher pitch
c.
(as modifier)
an octave leap
See also perfect (sense 9), diminished (sense 2), interval (sense 5)
2. prosody
a rhythmic group of eight lines of verse
3. (ˈɒkteɪv)
a.
a feast day and the seven days following
b.
the final day of this period
4.
the eighth of eight basic positions in fencing
5.
any set or series of eight
adjective
6.
consisting of eight parts
Word origin
C14: (originally: eighth day) via Old French from Medieval Latin octāva diēs eighth day (after a festival), from Latin octo eight
octave in American English
(ˈɑktɪv; ˈɑkˌteɪv)
noun
1.
a.
the eighth day following a church festival, counting the festival day as the first
b.
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
a.
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
b.
the interval of seven diatonic degrees between a tone and either of its octaves
c.
the series of tones contained within this interval, or the keys of an instrument producing such a series
d.
a tone and either of its octaves sounded together
e.
an organ stop producing tones an octave above those ordinarily produced by the keys struck
adjective
6.
consisting of eight, or an octave
7. Music
producing tones an octave higher
an octave key
Derived forms
octaval (ocˈtaval) (ɑkˈteɪvəl; ˈeɪktəvəl)
adjective
Word origin
OFr < L octava, fem. of octavus, eighth < octo, eight
Examples of 'octave' in a sentence
octave
Suddenly his instrument shot up an octave in an astonished squeak.
Ben Nimmo IN FORKBEARD'S WAKE: Coasting Round Scandinavia (2003)
His voice drops an octave, disappointed at this flippant question.
Times, Sunday Times (2016)
I suspect that his voice broadens an octave whenever he sees me.