There is not an existent word "themal". If you mean thermal, here are the definitions:

1.

[Latin thermae public baths, from Greek thermai,plural of thermē] : of, relating to, or marked by the presence of hot springs <thermal waters>

2.

a of, relating to, or caused by heat <thermalstress> <thermal insulation>

b : being or involving a state of matter dependent upon temperature <thermal conductivity> <thermal agitation of molecular structure>

c : having low energies of the order of those due to thermal agitation <thermal neutrons>

3.

designed (as with insulating air spaces) to prevent the dissipation of body heat <thermal underwear>