Of, relating to, or being the epoch of geologic time from about 2.6 million to 12,000 years ago, the older of the two epochs of the Quaternary Period. It is characterized by the alternate appearance and recession of northern glaciation, the appearance and worldwide spread of hominins, and the extinction of numerous land mammals, such as the mammoths, mastodons, and saber-toothed tigers. See Table at geologic time.
The Pleistocene Epoch.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.