Definition : nonsense —often used as an interjection
Lots of people questioned his argument, but he waved them aside. Fiddle faddle, said Mr. Mulcair.
— editorial, The Financial Post (Canada), 10 Dec. 2013
The word fiddle-faddle comes from a long tradition of words playfully coined by the process of reduplication: in this case, the word fiddlesticks got cut down and doubled with a vowel change. And it all happened quite a long time ago: our earliest evidence of fiddle-faddle in use is from 1577.