- thermal [thʉr′məl]adj.[Fr < Gr thermē, heat: see WARM]1. having to do with heat, hot springs, etc.2. warm or hot☆ 3. designating or of a loosely knitted material honeycombed with air spaces for insulation to help retain body heat [thermal underwear]n.a rising column of warm air, caused by the uneven heating of the earth or sea by the sunthermallyadv.
English World dictionary. V. Neufeldt. 2014.