1. Being in the process of passing out of use or usefulness; becoming obsolete.
2. Biology Becoming reduced during the course of evolution; vestigial or nearly vestigial. Used of an organ or other part of an organism.
[Latin obsolēscēns, obsolēscent-, present participle of obsolēscere, to fall into disuse : ob-, away; see OB- + solēre, to be accustomed to.]
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.