Webster's Revised Unabridged Dictionary · 1913

Thermal

Thermal , adjective

[Latin thermae hot springs, from Greek {not transcribed}, plural of {not transcribed} heat, from {not transcribed} hot, warm, {not transcribed} to warm, make hot; perhaps akin to Latin formus warm, and English forceps.]

1.
Of or pertaining to heat; warm; hot; as, the thermal unit; thermal waters.
The thermal condition of the earth. — J. D. Forbes
2.
caused by or affected by heat; as, thermal springs.
3.
designed to retain heat; as, thermal underwear.
Collocations (2)
Thermal conductivity or 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.