What is the language of Origin for word Bias?

The word "bias" originates from Middle French, where it was "biais". It then came into English in the 14th century.

The Middle French "biais" itself comes from the Old French "biais", which meant "slanting" or "oblique". This further derives from the Latin "biās", which also meant "slanting" or "oblique".

So, while the direct origin is Middle French, its root ultimately lies in the Latin language.