What is "to play first fiddle"

Fiddle \Fid"dle\ (f[i^]d"d'l), n. [OE. fidele, fithele, AS. fi[eth]ele; akin to D. vedel, OHG. fidula, G. fiedel, Icel. fi[eth]la, and perh. to E. viol. Cf. Viol.]

1. (Mus.) A stringed instrument of music played with a bow; a violin; a kit.

2. (Bot.) A kind of dock ( Rumex pulcher) with fiddle-shaped leaves; -- called also fiddle dock.

3. (Naut.) A rack or frame of bars connected by strings, to keep table furniture in place on the cabin table in bad weather.
   --Ham. Nav. Encyc.

   Fiddle beetle (Zo["o]l.), a Japanese carabid beetle ( Damaster blaptoides); -- so called from the form of the body.

   Fiddle block (Naut.), a long tackle block having two sheaves of different diameters in the same plane, instead of side by side as in a common double block.
   --Knight.

   Fiddle bow, fiddlestick.

   Fiddle fish (Zo["o]l.), the angel fish.

   Fiddle head, See fiddle head in the vocabulary.

   Fiddle pattern, a form of the handles of spoons, forks, etc., somewhat like a violin.

   Scotch fiddle, the itch. (Low)

   To play first fiddle, or To play second fiddle, to take a leading or a subordinate part. [Colloq.]