The Collaborative International Dictionary of English v.0.48:

Thermojunction \Ther`mo*junc"tion\, n. (Elec.)
   A junction of two dissimilar conductors used to produce a
   thermoelectric current, as in one form of pyrometer; a
   thermocouple.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

thermojunction
    n 1: a junction between two dissimilar metals across which a
         voltage appears