fid·dle / ˈfidl/ • n. 1. inf. a violin, esp. when used to play folk music.2. inf., chiefly Brit. an act of defrauding, cheating, or falsifying: a major mortgage fiddle.3. Naut. a contrivance, such as a raised rim, that prevents things from rolling or sliding off a table in bad weather.• v. inf. 1. [intr.] play the fiddle: (fiddling) country music with lots of fiddling and banjo playing. ∎  [tr.] play (a tune) on the fiddle.2. [intr.] touch or fidget with something in a restless or nervous way: Laura fiddled with her cup. ∎  tinker with something in an attempt to make minor adjustments or improvements: never fiddle with an electric machine that's plugged in. ∎  (fiddle around) pass time aimlessly, without doing or achieving anything of substance.3. [tr.] falsify (figures, data, or records), typically in order to gain money: everyone is fiddling their expenses.PHRASES: (as) fit as a fiddle in good health.play second fiddle to take a subordinate role to someone or something in a way often considered demeaning: she had to play second fiddle to the interests of her husband.DERIVATIVES: fid·dler n.

fiddle as fit as a fiddle in very good health. The phrase (with the related fine as a fiddle) is recorded from the early 17th century, and probably derives from the emphasis given by alliteration (compare the archaic fine as fivepence).
fiddle while Rome burns be concerned with relatively trivial matters while ignoring the serious or disastrous events going on around one; the original reference is to the behaviour of the emperor Nero, who according to Suetonius sang the whole of ‘The Sack of Ilium’ in his preferred stage costume to celebrate the beauty of the flames as Rome burned.

The first use of fiddle in this allusion is found in George Daniel's Trinarchodia (1649).
play second fiddle have a subordinate role to someone or something; be treated as less important than someone or something.

see also there's many a good tune played on an old fiddle.

fiddle stringed musical instrument played with a bow. OE. fiðele = (M)Du. vedel (veel), OHG. fidula (G. fiedel), ON. fiðla :- Gmc. *fiþula of obscure orig.; cf. VIOL, VIOLA2, VIOLIN, and medL. vidula, fidula, vitula, etc.
Hence vb. XIV. fiddler OE. fiðlere.

fiddle. Colloquial term for any kind of bowed instr., especially the vn., or in reference to its use as a ‘folk’ instr. (as in Mahler's 4th Sym. where a solo vn., specially tuned, is instructed to play wie ein Fiedel (‘like a fiddle’, in folk style). Also name for the medieval ancestor of the vn.