symphony (n.)

c. 1300, simphonie, 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 symphōnia "harmony, concord of sounds," from symphōnos "harmonious, agreeing in sound," from assimilated form of syn- "together" (see syn-) + phōnē "voice, sound" (from PIE root *bha- (2) "to speak, tell, say").

The original sense is obsolete; it was applied to everything from a small hurdy-gurdy to a bagpipe to a drum; a player on one was a symphoner. The meaning "pleasing combination of sounds, consonance agreeable to the ear, harmonic singing" in English is attested from late 14c.

The sense of "music in parts" is from 1590s. The meaning "elaborate orchestral composition in three or more movements" is attested from 1789.

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"]

Elliptical for symphony orchestra from 1926. Diminutive symphonette is recorded from 1947.