In common English usage a fiddle is always a violin. If someone says I play the fiddle they mean they play the violin - it is the only instrument to have this name in this sense. Confusingly fiddle is also a category of ethnomusicological reference for bowed chordophones, so such instruments from other cultures are both classified as fiddles and are referred to as such informally (and ethnocentrically - i.e. Chinese Fiddle, Black Sea Fiddle, Cactus Fiddle, Spike Fiddle, Horse Head Fiddle etc.) but never simply as the fiddle, and certainly not by the musicians who play them in their mother cultures.