Someone who is easily tricked or manipulated (or rather, played) by others. Usually too nice for their own good. Derived from the phrase "playing someone like a fiddle"
1. To cheat someone of money.
2. APpears in the UK sitcom "Blackadder" (series 3) as a rude word (when looking up the words "Fart, Fiddle, Fornicate" in Dr Johnson's first dictionary). Quite what 'fiddle' is intended to mean in this context is not clear.