octave n.

"1 more than seven, twice four; the number which is one more than seven; a symbol representing this number;" late 14c., eighte, earlier ehte (c. 1200), from Old English eahta, æhta, from Proto-Germanic *akhto (source also of Old Saxon ahto, Old Frisian ahta, Old Norse atta, Swedish åtta, Dutch acht, Old High German Ahto, German acht, Gothic ahtau), from PIE *okto(u) "eight" (source also of Sanskrit astau, Avestan ashta, Greek okto, Latin octo, Old Irish ocht-n, Breton eiz, Old Church Slavonic osmi, Lithuanian aštuoni). From the Latin word come Italian otto, Spanish ocho, Old French oit, Modern French huit. For spelling, see fight (v.).

Meaning "eight-man crew of a rowing boat" is from 1847. The Spanish piece of eight (1690s) was so called because it was worth eight reals (see piece (n.)). Figure (of) eight as the shape of a race course, etc., attested from c. 1600. To be behind the eight ball "in trouble" (1932) is a metaphor from shooting pool. Eight hours as the ideal length of a fair working day is recorded by 1845.

1580s, printer's word for sheets folded to make eight leaves, from Latin in octavo "in the eighth," ablative of octavus "eighth" from octo "eight" (see eight, and compare octave). Abbreviation is 8vo.

form of versification, 1820, Italian, "eight-lined stanza," literally "eighth rhyme," from ottava "eighth" (see octave + rhyme (n.)). A stanza of eight 11-syllable lines, rhymed a b a b a b c c, but in the Byronic variety the lines are typically 10-syllable English heroics.