In theology, monotheism (from Greek μόνος "one" and θεός "god") is the belief in the existence of one deity or God, or in the oneness of God. In a Western context, the concept of "monotheism" tends to be dominated by the concept of the God of the Abrahamic religions and the Platonic concept of God as put forward by Pseudo-Dionysius the Areopagite.
The concept of monotheism has largely been defined in contrast with polytheistic religions, and monotheism tends to overlap with other Unitary concepts, such as monism.
Ostensibly monotheistic religions may still include concepts of a plurality of the divine, for example the Christian Trinity, or the veneration of Saints, as well as the belief in "lesser spirits" such as angels or demons.
Historically, monotheism emerged gradually out of henotheistic and panentheistic notions from the Late Bronze Age, notably with pharaoh Akhenaten's Atenism. Monotheism historically became widespread as a belief system only during the Axial Age, and is associated with the philosophical and moral revolution of that age.