monad

UK: /ˈmɒnæd/ US: (mon′ad, mō′nad)

WordReference Random House Unabridged Dictionary of American English © 2025

mon•ad  (mon′ad, mō′nad), n. 

1. Microbiology [Biol.]
   • any simple, single-celled organism.
   • any of various small, flagellate, colorless ameboids with one to three flagella, esp. of the genus Monas.
2. Chemistry an element, atom, or group having a valence of one. Cf. dyad (def. 3), triad (def. 2a).
3. Philosophy
   • (in the metaphysics of Leibniz) an unextended, indivisible, and indestructible entity that is the basic or ultimate constituent of the universe and a microcosm of it.
   • (in the philosophy of Giordano Bruno) a basic and irreducible metaphysical unit that is spatially and psychically individuated.
   • any basic metaphysical entity, esp. having an autonomous life.
4. a single unit or entity.

• Greek (stem of monás): unity. See mon-, -ad¹
• Late Latin monad- (stem of monas)
• 1605–15;

mo•nad•ic  (mə nad′ik), mo•nad′i•cal, mo•nad′al, adj.  mo•nad′i•cal•ly, adv. 

Collins Concise English Dictionary © HarperCollins Publishers::

monad / ˈmɒnæd ˈməʊ-/ noun

1. ( -ads, -ades / -əˌdiːz/) any fundamental singular metaphysical entity, esp if autonomous
2. a single-celled organism, esp a flagellate protozoan
3. an atom, ion, or radical with a valency of one

Also called (for senses 1, 2): monas Etymology: 17th Century: from Late Latin monas, from Greek: unit, from monos alone