rheochord

from The Century Dictionary.

• noun A metallic wire used in measuring the resistance or varying the strength of an electric current, in proportion to the greater or less length of it inserted in the circuit.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A wire that can measure or vary the resistance of an electric circuit, or measure the variability of the current.