Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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