The Collaborative International Dictionary of English v.0.48:

Thermocouple \Ther"mo*cou`ple\, n.
   A thermoelectric couple.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

thermocouple
    n 1: a kind of thermometer consisting of two wires of different
         metals that are joined at both ends; one junction is at the
         temperature to be measured and the other is held at a fixed
         lower temperature; the current generated in the circuit is
         proportional to the temperature difference [syn:
         thermocouple, thermocouple junction]