Synarchism is a term which generally refers to "joint rule" or "harmonious rule".

Beyond this general definition, however, both "synarchism" and "synarchy" have been used to describe several different political processes in various contexts. Increasingly, the terms have been used by conspiracy theorists to mean rule by a secret elite.

The earliest recorded use of the term "synarchy" is attributed to Thomas Stackhouse (1677–1752), an English clergyman who used the word in his New History of the Holy Bible from the Beginning of the World to the Establishment of Christianity (published in two folio volumes in 1737). The attribution can be found in the Webster's Dictionary (the American Dictionary of the English Language, published by Noah Webster in 1828). Webster's definition for "synarchy" is limited entirely to "joint rule or sovereignty". The word is derived from the Greek stems "syn" meaning with or together and "archy" meaning rule.

The most substantial early use of the word "synarchy" comes from the writings of Alexandre Saint-Yves d'Alveydre (1842–1909), who used the term in his book La France vraie to describe what he believed was the ideal form of government. In reaction to the emergence of anarchist ideologies and movements, Saint-Yves elaborated a political formula which he believed would lead to a harmonious society. He defended social differentiation and hierarchy with collaboration between social classes, transcending conflict between social and economic groups: synarchy, as opposed to anarchy. Specifically, Saint-Yves envisioned a Federal Europe (as well as all the states it has integrated) with a corporatist government composed of three councils, one for academia, one for the judiciary, and one for commerce.