Thermal \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.

Source: Webster's Revised Unabridged Dictionary (1913)