[ad. Gr. τετράχορδον (sc. ὄργανον), a Greek musical instrument, f. τετρα-, TETRA- + χορδή string.]
1. An ancient musical instrument with four strings.
1603. Holland, Plutarch, Explan. Words, Tetrachord, an instrument in old time of foure strings.
1814. Maun. & Cust., in Ann. Reg., 490/1. Most of the Greek women sing in a pleasing manner, accompanying themselves with a tetrachord, the tones of which are an excellent support to the voice.
1849. Donaldson, Theat. Greeks (ed. 6), I. ii. 15. Terpander … substituted the seven-stringed cithara for the old tetrachord.
2. Mus. A scale-series of four notes, being the half of an octave. † b. The interval between the first and last notes of this series; a perfect fourth.
1603. Holland, Plutarch’s Mor., 1254. It was not for ignorance that in the Dorian tunes they forbare this Tetrachord.
1694. W. Holder, Harmony, iv. (1731), 66. (Table of Intervals), 4th, Diatessaron, Tetrachord.
1704. J. Harris, Lex. Techn., I. Tetrachord, in Musick, is a Concord or Interval of 3 Tones. The Tetrachord of the Ancients was a rank of four Strings.
1847. Grote, Greece, II. xvi. III. 285. Such were the three modes or scales, each including only a tetrachord, upon which the earliest Greek masters worked.
1890. Athenæum, 4 Jan., 24/3. The tetrachord [on an Arab lute] thus comprised C, D, E flat, E, and F.
c. transf. A stanza of four lines. rare.
1817. N. Drake, Shakspeare, I. 54. The Octant, of two tetrachorus of disjunct alternate rhime. Ibid., 55. Three tetrachords in alternate rhime.
Hence Tetrachordal a., of or pertaining to a tetrachord or tetrachords. Also ǁ Tetrachordon [see quot.], an instrument like a cottage pianoforte in form, in which the strings are pressed against a revolving cylinder to produce the tone.
1850[?]. Sarah A. Glover (title), Manual, containing a development of the *tetrachordal System.
1876. Stainer & Barrett, Dict. Mus. Terms, s.v. Tonic Sol-fa, Miss Sarah A. Glover, of Norwich, about thirty years ago projected and taught … a system which she called the tetrachordal system, which was the Tonic Sol-fa notation in its original form. Ibid., *Tetrachordon … [so] called … from an idea that its sounds are similar to those produced by a string quartet.
