CHORUS properly a dance, and especially the sacred dance, accompanied by song, of ancient Greece at the festivals of the gods. The word seems originally to have referred to a dance in an enclosure, and is therefore usually connected with the root appearing in Gr., hedge, enclosure, Lat. hortus, garden, and in the Eng. "yard," "garden" and "garth." Of choral dances in ancient Greece other than those in honour of Dionysus we know of the Dance of the Crane at Delos, celebrating the escape of Theseus from the labyrinth, one telling of the struggle of Apollo and the Python at Delphi, and one in Crete recounting the saving of the new-born Zeus by the Curetes. In the chorus sung in honour of Dionysus the ancient Greek drama had its birth. From that of the winter festival, consisting of the or band of revellers, chanting the "phallic songs," with ribald dialogue between the leader and his band, sprang "comedy," while from the dithyrambic chorus of the spring festival came "tragedy." For the history of the chorus in Greek drama, with the gradual subordination of the lyrical to the dramatic side in tragedy and its total disappearance in the middle and new comedy, see Drama: Greek Drama.
The chorus as a factor in drama survived only in the various imitations or revivals of the ancient Greek theatre in other languages. A chorus is found in Milton's Samson Agonistes. The Elizabethan dramatists applied the name to a single character employed for the recitation of prologues or epilogues. Apart from the uses of the term in drama, the word "chorus" has been employed chiefly in music. It is used of any organized body of singers, in opera, oratorio, cantata, etc., and, in the form "choir," of the trained body of singers of the musical portions of a religious service in a cathedral or church. As applied to musical compositions, a "chorus" is a composition written in parts, each to be sung by groups of voices in a large body of singers, and differs from "glee" (q.v.), where each part is for a single voice. The word is also used of that part of a song repeated at the close of each verse, in which the audience or a body of singers may join with the soloist.
In the early middle ages the name chorus was given to a primitive bagpipe without a drone. The instrument is best known by the Latin description contained in the apocryphal letter of St Jerome, ad Dardanum: "Chorus quoque simplex, pellis cum duabus cicutis aereis, et per primam inspiratur per secundam vocem emittit." Several illuminated MSS.  from the 9th to the 11th century give fanciful drawings, accompanied by descriptions in barbarous Latin, evidently meant to illustrate those described in the letter to Dardanus. The original MS., probably an illustrated transcript of this letter, which served as a copy for the others, was apparently produced at a time when the Roman bagpipe (tibia utricularia) had fallen into disuse in common with other musical instruments, and was unknown except to the few. The Latin description given above is correct and quite unmistakable to any one who knows the primitive form of bagpipe; the illustrations must therefore represent the effort of an artist to depict an unknown instrument from a description. Virdung, Luscinius and Praetorius seem to have had access to a MS. of the Dardanus letter now lost, and to have reproduced the drawings without understanding them. In a MS. of the 14th century at the British Museum,  containing a chronicle of the world's history to the death of King Edward I., the chorus is mentioned and described in similar words to those quoted above; in the margin is an elementary sketch of a primitive bagpipe with blowpipe and chaunter with three holes, but no drone. Bagpipes with drones abound on sculptured monuments and in miniatures of that century. Gerbert gives illustrations of the fanciful chorus from the Dardanus letter and of two other instruments of later date; one of these represents a musician playing the Platerspiel, the other the bagpipe known as chevrette, in which the whole skin of the animal (a kid or pig), with head and feet, has been used for the bag. Edward Buhle,  in his admirable work on the musical instruments in the illuminated MSS. of the middle ages, points out that Gerbert,  who gives the dates of his two MSS. as "6th and 9th centuries," has a singular method of reckoning the date of a MS.; he refers to the age of a MS. at the time of writing (18th century), not to the date at which it was produced. The MS. containing the two figures of musicians mentioned above, instead of being ascribed to the 6th century, was six centuries old when Gerbert wrote in 1774, and dates therefore from the 12th century. It is interesting to note that Giraldus Cambrensis  mentions the chorus as one of the three instruments of Wales and Scotland, ascribing superior musical skill to the latter. Historians record that King James I. of Scotland was renowned for his skill as a performer on various musical instruments, one of which was the chorus.  This bears out the traditional belief that the bagpipe had been a Scottish attribute from the earliest times. The word "chorus" occurs once or twice in French medieval poems with other instruments, but without indication as to the kind of instrument thus designated. The word was probably the French equivalent for the Platerspiel.
See also G. Kastner, Danses des morts (pp. 200 to 202, pl. xv., No. 103); and Dom Pedro Cerone, El Melopeo y maestro (Naples, 1613), p. 248.
 The MSS. are a psalterium, 9th century, Bibl. publique, Angers, fol. 13a; Boulogne Psalterium glossatum c. A.D. 1000, MS. No. 20, Bibl. publique. For reproduction of musical instruments see Annales archéologiques, tome iv. (1846), p. 38; Cotton MS., Tiberius C. vi., 10th to 11th century, fol. 16b, British Museum, illustrated in Strutt's Horda Angel-cynnan, vol. ii. pls. xx. and xxi.; MS. psalter of St Emmeran, now in Munich Staatsbibliothek, clm. 14523, fol. 51b, 10th century, illustrated by Gerbert, De Cantu et Mus. Sacra, tome ii. pi. xxiii.; Paris, Bibl. Nat. Fonds Latin, 7211, 1Oth century, fol. 150 and 151a.
 Cotton MS., Nero D. ii. f. 15a, Chronicon ab orbe condito ad obitum Regis Edwardi I., 1307.
 Die musikalischen Instrumente in den Miniaturen des frühen Mittelalters, part i. "Die Blasinstrumente" (Leipzig, 1903), p. 7, note 1.
 Op. cit. (1774), tome ii. pl. xxv. No. 13, pp. 130, 151, 152, and pl. xxxi. No. 12.
 Topographia Hiberniae, cap. xi.
 Scotichronicon (Fordun and Bower), xvi. 28; and Dalyell, Musical Memoirs of Scotland, p. 47, pls. x. and xi.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)