"stringed musical instrument, violin," late 14c., fedele, fydyll, fidel, earlier fithele, from Old English fiðele "fiddle," which is related to Old Norse fiðla, Middle Dutch vedele, Dutch vedel, Old High German fidula, German Fiedel "a fiddle;" all of uncertain origin.
The usual suggestion, based on resemblance in sound and sense, is that it is from Medieval Latin vitula "stringed instrument" (source of Old French viole, Italian viola), which perhaps is related to Latin vitularia "celebrate joyfully," from Vitula, Roman goddess of joy and victory, who probably, like her name, originated among the Sabines [Klein, Barnhart]. Unless the Medieval Latin word is from the Germanic ones.
FIDDLE, n. An instrument to tickle human ears by friction of a horse's tail on the entrails of a cat. [Ambrose Bierce, "The Cynic's Word Book," 1906]
Fiddle has been relegated to colloquial usage by its more proper cousin, violin, a process encouraged by phraseology such as fiddlesticks (1620s), contemptuous nonsense word fiddle-de-dee (1784), and fiddle-faddle. Century Dictionary  reports that fiddle "in popular use carries with it a suggestion of contempt and ridicule." Fit as a fiddle is from 1610s.
1878, geestring, "loincloth worn by an American Indian," originally the string that holds it up, etymology unknown. The spelling with G (1882) is perhaps from influence of violin string tuned to a G (in this sense G string is first recorded 1831), the lowest and heaviest of the violin strings. First used of women's attire 1936, with reference to strip-teasers.
I AM the spirit of the silver "G":
I am silvered sadness,
I am moonlit gladness,
I am that fine madness
Of reverence half, and half of ecstasy
[from "Spirit of the 'G' String," Alfred L. Donaldson, in "Songs of My Violin," 1901]
"an occasional pastime, an activity other than that for which one is well-known, or at which one excells," 1963, from French, literally "Ingres' violin," from the story that the great painter preferred to play his violin (badly) for visitors instead of showing them his pictures.
Une légende, assez suspecte, prétend que le peintre Ingres état plus fier de son jeu sur le violon, jeu qui était fort ordinaire, que de sa peinture, qui l'avait rendu illustre. [Larousse du XXe Siecle, 1931]
town in Lombardy, from Cenomani, name of a Gaulish people who lived there in Roman times, or perhaps from a Celtic word meaning "garlic" (compare Old Irish crim, Welsh craf). From 1762 as "violin made at Cremona by the Amati family (late 16c.-early 17c.) or Stradivarius (early 18c.)." Related: Cremonese.