Definition of octave noun from the Oxford Advanced Learner's Dictionary

 

octave

 noun
noun
BrE BrE//ˈɒktɪv//
 
; NAmE NAmE//ˈɑːktɪv//
 
(music)
 
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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 Origin Middle 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’.
See the Oxford Advanced American Dictionary entry: octave