1. An enclosure in which energy in a nonthermal form is converted to heat, especially such an enclosure in which heat is generated by the combustion of a suitable fuel.
2. An intensely hot place: the furnace of the sun; an attic room that is a furnace in the summer.
3. A severe test or trial: endured the furnace of his friends' blame after the accident.
[Middle English fourneyse, from Old French fornaise, variant of earlier fornais, from Latin fornāx, fornāc-, oven; see gwher- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.