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oc·tave (ŏktĭv, -tāv)
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n.
1. Music
a. The interval of eight diatonic degrees between two tones of the same name, the higher of which has twice as many vibrations per second as the lower.
b. A tone that is eight diatonic degrees above or below another given tone.
c. Two tones eight diatonic degrees apart that are sounded together.
d. The consonance that results when two tones eight diatonic degrees apart are sounded.
e. A series of tones included within this interval or the keys of an instrument that produce such a series.
f. An organ stop that produces tones an octave above those usually produced by the keys played.
g. The interval between any two frequencies having a ratio of 2 to 1.
2. Ecclesiastical
a. The eighth day after a feast day, counting the feast day as one.
b. The entire period between a feast day and the eighth day following it.
3. A group or series of eight.
4.
a. A group of eight lines of poetry, especially the first eight lines of a Petrarchan sonnet. Also called octet.
b. A poem or stanza containing eight lines.
5. Sports A rotating parry in fencing.

[Middle English, eighth day after a feast day, from Old French, from Medieval Latin octāva (diēs), from Latin, feminine of octāvus, eighth, from octō, eight; see oktō(u) in the Appendix of Indo-European roots.]

oc·taval (ŏk-tāvəl, ŏktə-vəl) adj.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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