Monad

Monad (μονάς monas) is a Greek word for "unit". With the Pythagoreans it was a term for Divinity, the source or the One.

In Theosophy monad refers to the two highest principles atman and buddhi, which engage in a process of evolution to emerge as a triad after assimilating the essence of manas during the stage of human evolution:

Monad (Gr.). The Unity, the one ; but in Occultism it often means the unified triad, Atma-Buddhi-Manas, or the duad, Atma-Buddhi, that immortal part of man which reincarnates in the lower kingdoms, and gradually progresses through them to Man and then to the final goal— Nirvâna.