The Monad figure is one of the most mysterious symbols in Alchemy. It contains all the glyphs of the archetypal planets of Saturn, Jupiter, Mars, Venus, Mercury, Moon, and the Sun. By tracing the connecting lines and circles in different ways, one can locate the symbols of these seven sacred planets and thereby reveal the invisible sevenfold force behind Nature.
According to John Dee, the 16th century Alchemist who served Queen Elizabeth the First, the Monad "imbued the astronomical symbols with immortal life" and allowed their meaning to be expressed "most eloquently in any tongue and to any nation." The Monad could express all this because the celestial planets were reduced to their essential “mystical proportions" within it. The word “monad” comes from the Greek word μόνος, which means "one as a unique and ultimate unity." The followers of Pythagoras believed that the Monad was the first thing that came into existence.
Excerpt from “Everyday Alchemy” by Dennis William Huack:
The most powerful symbol in all of alchemy is a rather odd-looking cipher that looks like a little stick man (shown at right). Known as the Monas Hieroglyphica (Hieroglyphic Monad), it is the most secret and sacred symbol in alchemy. It is so unique and powerful that the symbol itself is thought to carry its own spirit, which is evoked every time it is written down or constructed. The spiritual presence carried by the symbol is said to have its own life force and intelligence and act like a guide to alchemists pursuing the Great Work. In many ways, the symbol embodies all the teachings and spirit of Thoth (Hermes) himself. The secret cipher is a treasure map to something wonderful hidden within us.
There is no better reminder of Hermetic principles in daily life than a quick meditation on this easy-to-remember insignia. Once you open up a relationship with this symbol, it will be with you always to lead you to the higher reality of any situation you encounter in the everyday world. This idea is evident in the Latin caption In Hoc Signo Vinces (“In this sign you will conquer”) that the alchemists gave to this symbol.
Sources:
(1) Everyday Alchemy by Dennis William Hauck
The Secret Teachings of All Ages by Manly P. Hall