What is Fiddle ?
Fiddle is (verb) 1. to fiddle with something to play idly with something She was fiddling with her bracelet during the whole interview. He fiddled with the radio and managed to get it to work. 2. to play the fiddle He was fiddling away at an Irish dance. 3. to keep information about money in a dishonest way The company caught him fiddling his expense account. She tried to fiddle her tax return. (noun) 1. a violin He plays the fiddle at country dances. fit as a fiddle very fit He’s over eighty and still as fit as a fiddle. to play second fiddle to someone to be in a weaker position than someone else He always plays second fiddle to his wife. 2. dishonest or illegal dealings (informal.) The whole thing’s a fiddle to get money from the EU. on the fiddle trying to make money illegally
source: Easier English, Student Dictionary Upper Intermediate Level