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.
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