A theory of the thermodynamic behavior of matter, especially the relationships among pressure, volume, and temperature in gases, based on the dependence of temperature on the kinetic energy of the rapidly moving particles of a substance. The theory uses statistical mechanics under the presumption that energy and momentum are conserved in all collisions between particles.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.