The Collaborative International Dictionary of English v.0.48:

Rheochord \Rhe"o*chord\, n. [Gr. "rei^n to flow + ??? chord.]
   (Elec.)
   A metallic wire used for regulating the resistance of a
   circuit, or varying the strength of an electric current, by
   inserting a greater or less length of it in the circuit.
   [1913 Webster]