ther·mal (thûr?m?l)adj.1. Of, relating to, using, producing, or caused by heat.2. Intended or designed in such a way as to help retain body heat: thermal underwear.n. A rising current of warm air.ther?mal·ly adv.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.thermal (????m?l) adj1. (General Physics) Also: thermic of, relating to, caused by, or generating heat or increased temperature2. hot or warm: thermal baths; thermal spring. 3. (Textiles) (of garments or fabrics) specially designed so as to have exceptional heat-retaining propertiesn4. (Physical Geography) meteorol a column of rising air caused by local unequal heating of the land surface, and used by gliders and birds to gain height5. (Clothing & Fashion) (plural) thermal garments, esp underclothes ?thermally advCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ther?mal (???r m?l) adj. 1. Also, thermic. of, pertaining to, or caused by heat or temperature: thermal energy. 2. of, pertaining to, or of the nature of hot or warm springs: thermal waters. 3. designed to aid in or promote the retention of body heat: a thermal blanket; thermal underwear. n. 4. a rising air current caused by heating from the underlying surface. 5. thermals, clothing, esp. underwear, designed to help retain body heat. [1750?60] ther?mal?ly, adv. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.ther·mal (thûr?m?l)Adjective Relating to heat.Noun A current of warm air that rises because it is less dense than the air around it.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.thermalA rising column of warm air.Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited