An exclamation expressing doubt, dismissal, or annoyance; also literally the bow used to play a fiddle.
The literal meaning is the stick used with a violin/fiddle. As an exclamation, it's likely a euphemistic substitution for stronger curses, disguising the swear word 'fiddlesticks' sounds like.
Fiddlesticks is a brilliant piece of language history—it's a euphemism that works by sound similarity to a more offensive word, but it's so old and clever that most people just know it as a silly Victorian way to say 'nonsense' without realizing it's coded language.
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