E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Fiddle (Latin, fidis or fides).
He was first fiddle. Chief man, the most distinguished of the company.
1
To play second fiddle. To take a subordinate part. The allusion is to the leader of concerts, who leads with a fiddle.
2
The Scotch fiddle or Caledonian Cremna. The itch. As fiddlers scratch with a bow the strings of a fiddle, so persons suffering from skin-irritation keep scratching the part irritated.