There's the Swedish word fela (en fela) which is closer in meaning to fiddle, but I have a feeling that fiddle is used more widely than fela, so there's some overlap.

We have three words: violin, fiol, and fela.

When playing folk music, you almost always say "fiol". In a professional symphony orchestra, you say "violin". When you take lessons and play in your free time, most often "fiol" but sometimes "violin", especially when you want to distinguish from the "viola/altfiol".

I would prefer på onsdagar myself.