Monad

n. [ L. monas, -adis, a unit, Gr. &unr_;, &unr_;, fr. mo`nos alone. ] 1. An ultimate atom, or simple, unextended point; something ultimate and indivisible. [ 1913 Webster ]

2. (Philos. of Leibnitz) The elementary and indestructible units which were conceived of as endowed with the power to produce all the changes they undergo, and thus determine all physical and spiritual phenomena. [ 1913 Webster ]

3. (Zool.) One of the smallest flagellate Infusoria; esp., the species of the genus Monas, and allied genera. [ 1913 Webster ]

4. (Biol.) A simple, minute organism; a primary cell, germ, or plastid. [ 1913 Webster ]

5. (Chem.) An atom or radical whose valence is one, or which can combine with, be replaced by, or exchanged for, one atom of hydrogen. [ 1913 Webster ]

Monad deme (Biol.), in tectology, a unit of the first order of individuality. [ 1913 Webster ]