c. 1600, "area in an ancient theater for the chorus," from Latin orchestra, from Greek orkhēstra, semicircular space where the chorus of dancers performed, with suffix -tra denoting place + orkheisthai "to dance," perhaps an intensive of erkhesthai "to go, come," but not all experts accept that (see Beekes).

In ancient Rome, orchestra referred to the place in the theater reserved for senators and other dignitaries. Meaning "group of musicians performing at a concert, opera, etc." is recorded by 1720, so called because they occupy the position of the orchestra relative to the stage ; that of "part of theater in front of the stage" is from 1768 in English.

Some related words still retain the "dancing" sense: Orchestic "of or pertaining to dancing" (1712), also orchestric (1740).

"pertaining to an orchestra; suitable for performance by an orchestra," 1811, from orchestra + -al (1).

1840, "the act, process, or art of arranging music for an orchestra," from French orchestration (see orchestrate). U.S. slang sense of "an overcoat" is by 1940.

"to compose or arrange (music) for an orchestra," 1855, back-formation from orchestration. The figurative sense ("to coordinate, combine harmoniously") is attested from 1883. Related: Orchestrated; orchestrating.

"composition for two or more solo instruments, or one principal instrument accompanied by a large or small orchestra," 1730, from Italian concerto (see concert (n.)). Concerto grosso is attested from 1724. Diminutive concertino is from 1857; earlier it meant "the principal instruments in a concerto or concertante" (1819).

c. 1300, a name given to various types of musical instruments, from Old French simphonie, sifonie, simfone "musical harmony; stringed instrument" (12c., Modern French symphonie) and directly from Latin symphonia "a unison of sounds, harmony," from Greek symphonia "harmony, concord of sounds," from symphonos "harmonious, agreeing in sound," from assimilated form of syn- "together" (see syn-) + phōnē "voice, sound," from PIE root *bha- (2) "to speak, tell, say."

Meaning "harmony of sounds" in English is attested from late 14c.; sense of "music in parts" is from 1590s. "It was only after the advent of Haydn that this word began to mean a sonata for full orchestra. Before that time it meant a prelude, postlude, or interlude, or any short instrumental work." ["Elson's Music Dictionary"] Meaning "elaborate orchestral composition" first attested 1789. Elliptical for "symphony orchestra" from 1926. Diminutive symphonette is recorded from 1947.

c. 1600, "stage of an ancient theater," from Latin proscaenium, from Greek proskēnion "the space in front of the scenery," also "entrance of a tent," from pro "in front, before" (see pro-) + skēnē "stage, tent, booth" (see scene). Modern sense of "space between the curtain and the orchestra" (often including the curtain and its framework) is attested from 1807. Hence, figuratively, "foreground, front" (1640s).