Definition of "tetrachord" []

• Music A series of four diatonic tones encompassing the interval of a perfect fourth. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Now then, these intervals of tones and semitones of the tetrachord are a division introduced by nature in the case of the voice, and she has defined their limits by measures according to the magnitude of the intervals, and determined their characteristics in certain different ways."
• "Thus it appears that it was Didymus, and not Ptolemy, who proposed the tuning of the tetrachord which is now accepted as correct."
• "With the Greeks the tetrachord was the unit of analysis as the octave is with us to-day, and all Greek scales are capable of division into two tetrachords, the arrangement of the intervals between the tones in each tetrachord differentiating one scale from another, but the tetrachords themselves always consisting of groups of four tones, the highest being a perfect fourth above the lowest.] [Illustration: Fig. 53.]"