1. microbiology single-celled microorganism: a microorganism consisting of just one cell, especially a flagellate protozoan. Genus Monas.
2. chemistry atom with valence of one: an atom or chemical group that has a valence of one
3. philosophy basic entity in metaphysics of Leibnitz: in the metaphysics of Leibnitz, an indivisible indestructible unit that is the basic element of reality and a microcosm of it
[Mid-16th century. Directly or via French monade< late Latin monad-< Greek monos "single"]
