Originally, a patriarch was a man who exercised autocratic authority as a pater familias over an extended family. The system of such rule of families by senior males is termed patriarchy. This is a Greek word, a compound of πατριά (patria), "lineage, progeny", esp. by the father's side (which derives from the word πατήρ – patēr meaning "father") and ἄρχων (archon) meaning "leader", "chief", "ruler", "king", etc.
Abraham, Isaac, and Jacob are referred to as the three patriarchs of the people of Israel, and the period during which they lived is termed the Patriarchal Age. It originally acquired its religious meaning in the Septuagint version of the Bible.
The word has acquired specific ecclesiastical meanings. In particular, the highest-ranking bishops in Eastern Orthodoxy, Oriental Orthodoxy, the Roman Catholic Church (above Major Archbishop and Primate), and the Assyrian Church of the East are termed Patriarchs (and in certain cases also popes). The office and ecclesiastical circumscription (comprising one or more provinces, though outside his own (arch)diocese he is often without enforceable jurisdiction) of such a Patriarch is termed a Patriarchate. Historically, a Patriarch may often be the logical choice to act as Ethnarch, representing the community that is identified with his religious confession within a state or empire of a different creed (as Christians within the Ottoman Empire).