\Ther"mal\, a. [L. thermae hot springs, fr. Gr. ?, pl.
of ? heat, fr. ? hot, warm, ? to warm, make hot; perhaps akin
to L. formus warm, and E. forceps.]
Of or pertaining to heat; warm; hot; as, the thermal unit;
thermal waters.
      The thermal condition of the earth.      --J. D.
                                               Forbes.
{Thermal conductivity}, {Thermal spectrum}. See under
   {Conductivity}, and {Spectrum}.
{Thermal unit} (Physics), a unit chosen for the comparison or
   calculation of quantities of heat. The unit most commonly
   employed is the amount of heat necessary to raise the
   temperature of one gram or one pound of water from zero to
   one degree Centigrade. See {Calorie}, and under {Unit}.