(according to a legend widely believed in the Middle Ages) a woman in male disguise who (c.1100) became a distinguished scholar and then pope, reigned for more than two years, and died after giving birth to a child during a procession.
Definition of Pope Joan in US English:
Pope Joan
proper nounˌpōp ˈjōn
(according to a legend widely believed in the Middle Ages) a woman in male disguise who (c.1100) became a distinguished scholar and then pope, reigned for more than two years, and died after giving birth to a child during a procession.