from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun A sequence of six tones with a semitone in the middle, the others being whole tones, that was used in medieval music.
from The Century Dictionary.
- noun In Greek music: A diatonic series of six tones.
- noun The interval of a major sixth.
- noun An instrument with six strings.
- noun In medieval music, a diatonic series of six tones, containing four whole steps and one half-step (between the third and fourth tones).
from the GNU version of the Collaborative International Dictionary of English.
- noun (Mus.) A series of six notes, with a semitone between the third and fourth, the other intervals being whole tones.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun music A series of six tones denoted with the syllables ut-re-mi-fa-sol-la separated by seconds, the only of which that is a minor second being mi-fa.
from The American Heritage® Dictionary of the English Language, 4th Edition
"hexachord" on which the present scale was perfected.
Of a similar nature is Ut queant laxis, for five voices, in which the tenor sings the isolated notes of the hexachord between snatches of four-voice polyphony.
Running longitudinally, there are four channels in it if it is a tetrachord; six, if it is a hexachord; eight, if it is an octachord.
It will be observed that this hymn provided syllables only for the six tones of the _hexachord_ then recognized; when the octave scale was adopted (early in the sixteenth century) the initial letters of the last line (s and i) were combined into a syllable for the seventh tone.
Commencing with G, which was the lowest note of the system in Hucbald's time, the first hexachord was formed of G A B C D E; the second, following the example of the Greeks, he made to overlap the first, namely,
The next three hexachords were treated in the same manner; the last or seventh hexachord was merely a repetition of the first and the fourth.
Just as in mediaeval times each hexachord commenced with _ut_, so now every octave of our tonal system commences with _do_.
In order to make this hexachord identical in structure with, the first and second, he flatted the B, thus making the succession of notes, F G A B [flat] C D.
Following out his system, he applied the newly acquired syllables to each of the hexachords -- for instance, the lowest hexachord, G A B C D E, which was called hard, became _ut re mi fa sol la_; the second, which was called natural, C D E F
For the fourth hexachord, which was called hard, this B was again raised a semitone.