Source : Webster's Revised Unabridged Dictionary (1913)

Thermotension \Ther`mo*ten"sion\, n. [Thermo- + tension.]
   A process of increasing the strength of wrought iron by
   heating it to a determinate temperature, and giving to it,
   while in that state, a mechanical strain or tension in the
   direction in which the strength is afterward to be exerted.