Often used as an exclamation, fiddlefaddle means balderdash; trivial nonsense. It is falling out of favour and seems to have been largely superseded by far less polite words. My spellchecker prefers it to be written fiddle faddle as two separate words. Having hit the autocorrect button to do that it then tells me faddle is not a word. Fiddlefaddle!
Fiddlefaddle is also a verb though I have never heard it used as such. It means to fritter away one's time; to fuss or waste time, especially over trivial matters.