I. ˈäktə̇v, -tēv, -ˌtāv noun
( -s )
Etymology: Middle English, from Medieval Latin octava, from Latin, feminine of octavus eighth, from octo eight — more at eight
1.
a. : the eighth day counting the festival day after a church festival
b. : the eight day period beginning with the festival day
2.
a. : a stanza of eight lines : ottava rima
b. : the first two quatrains or first eight verses of a sonnet — called also octet ; compare sestet
3.
a. : a musical interval embracing eight diatonic degrees
b. : a tone or note at this interval
c. : the harmonic combination of two tones an octave apart
d. : the whole series of notes, tones, or digitals comprised within this interval and forming the unit of the modern scale
e. : an organ stop giving tones an octave above those corresponding to the digitals
4. : a parry or guard position in fencing defending the lower outside target in which the hand is to the right in a position of supination with the tip of the blade directed at the opponent's knee — compare seconde
5. : a group of eight
an octave of oarsmen
6. in a spectrum of vibrations : an interval analogous to the musical octave and being such that the frequencies at its beginning and end are to each other as 1 : 2
the visible or photic portion of the 60 or more octaves of the electromagnetic spectrum of radiant energy, extending from wireless waves to cosmic rays, constitutes about 1 octave and has wavelengths ranging from the red end of the spectrum (7700A) to the extreme violet end (about 4000A) — Charles Sheard
7.
a. : a cask for wine holding 1/8 pipe
b. : a unit of liquid capacity equal to 1/8 pipe or 13 1/2 gallons
8. archaic : a series of eight chemical elements in order of increasing atomic weights
II. adjective
1. : consisting of eight units
2. : sounding or producing sounds at the octave
an octave organ stop