octave
noun /ˈɒktɪv/
  /ˈɑːktɪv/
 (music)- the difference (the interval) between the first and last notes in a series of eight notes on a scale- to play an octave higher
- Orbison's vocal range spanned three octaves.
 Word OriginMiddle English (originally referring to a period of eight days beginning with the day of a Church festival): via Old French from Latin octava dies ‘eighth day’.