The term 'Supreme Egyptian Deity' refers to two gods, Amon-Ra and Amen-Ra. Amon-Ra was the god of the sun, air, and fertility, while Amen-Ra was the god of the moon and the underworld. Both gods were worshiped in ancient Egypt and were considered to be the most powerful deities in the pantheon. They were often depicted as a composite deity, with Amon-Ra representing the sun and Amen-Ra representing the moon. Together, they were seen as the ultimate source of power and authority in ancient Egypt.