Monad (philosophy), a term meaning “unit”, used by philosophers to signify a variety of entities, originally the God and later such things as genus.  “Monad” means that which is one, has no parts and is therefore indivisible. These are the fundamental existing things, according to Leibniz. His theory of monads is meant to be a superior alternative to the theory of atoms that was becoming popular in natural philosophy at the time.

https://iep.utm.edu/leib-met/