All 3 Uses of

octave
in
The Hunchback of Notre Dame

There were continual outbursts, melodies, unexpected cadences, then simple phrases strewn with aerial and hissing notes; then floods of scales which would have put a nightingale to rout, but in which harmony was always present; then soft modulations of octaves which rose and fell, like the bosom of the young singer.†
Chpt 1.2.3 *

You can follow the dialogue, by turns grave and shrill, of the treble and the bass; you can see the octaves leap from one tower to another; you watch them spring forth, winged, light, and whistling, from the silver bell, to fall, broken and limping from the bell of wood; you admire in their midst the rich gamut which incessantly ascends and re-ascends the seven bells of Saint-Eustache; you see light and rapid notes running across it, executing three or four luminous zigzags, and vanishing like flashes of lightning.†
Chpt 1.3.2

But when he had set them to swinging, when he felt that cluster of bells moving under his hand, when he saw, for he did not hear it, the palpitating octave ascend and descend that sonorous scale, like a bird hopping from branch to branch; when the demon Music, that demon who shakes a sparkling bundle of strette, trills and arpeggios, had taken possession of the poor deaf man, he became happy once more, he forgot everything, and his heart expanding, made his face beam.†
Chpt 2.7.3

Definition:

an interval of tones with the pitch at the high end being twice that at the low end -- 8 notes on the familiar diatonic scale