1. Philosophy An indivisible, impenetrable unit of substance viewed as the basic constituent element of physical reality in the metaphysics of Leibniz.
2. Biology A single-celled microorganism, especially a flagellate protozoan formerly classified in the taxonomic group Monadina.
[Latin monas, monad-, unit, from Greek, from monos, single; see men-4 in the Appendix of Indo-European roots.]
mo·nadic (mə-nădĭk), mo·nadi·cal adj.
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.