late 13c., "musical instrument, mechanical apparatus for producing musical sounds," from Old French instrument, enstrument "means, device; musical instrument" (14c., earlier estrument, 13c.) and directly from Latin instrumentum "a tool, an implement; means, furtherance; apparatus, furniture; ornament, dress, embellishment; a commission, authorization; a document," from instruere "arrange, prepare, set in order; inform, teach," literally "to build, erect," from in- "on" (from PIE root *en "in") + struere "to pile, build" (from PIE *streu-, extended form of root *stere- "to spread").
The word in other Germanic languages also is from French. In English the meaning "a means, an agency" is from mid-14c. The sense of "hand-tool, implement, utensil, something used to produce a mechanical effect" is from early 14c. "Now usually distinguished from a tool, as being used for more delicate work or for artistic or scientific purposes" [OED]. The legal meaning "written document by which formal expression is given to a legal act" is from early 15c. Formerly also used of body parts or organs with special functions.
In wyfhode I wol vse myn Instrument As frely as my makere hath it sent. [Chaucer, "Wife of Bath's Prologue"]
type of ancient stringed instrument, the accompanying instrument for psalms, c. 1300, sautrie, from Old French psalterie (12c.) and directly from Latin psalterium "stringed instrument," from Greek psaltērion "stringed instrument," from psallein "play on a stringed instrument, pull, pluck" (see psalm).
From c. 1200 in English in Latin form salteriun. It was similar to a harp, but of different shape and means of obtaining resonance (having a sound-board behind and parallel with the strings). Related: Psalterial; psalterian.
stringed musical instrument played with a bow, c. 1500, vial, from Old French viole, viol "stringed instrument like a fiddle," from Old Provençal viola (see viola).
"the Book of Psalms," Middle English sauter, psauter, from Old English saltere, psaltere, Old French sautier, psaltier, and directly from Church Latin psalterium "the songs of David," in secular Latin, "stringed instrument played by twanging," from Greek psaltērion "stringed instrument, psaltery, harp," from psallein "to pluck, play on a stringed instrument" (see psalm).