[kawn-stuh
n-tan] 
| an alloy containing approximately 55 percent copper and approximately 45 percent nickel, used for electrical resistance heating and thermocouples. |
| con·stan·tan (kŏn'stən-tān') n. An alloy of 45 percent nickel and 55 percent copper, used chiefly in electrical instruments because of its constant resistance under variations of temperature. [From constant.] |