Ethnonym is a related term of endonym.

As nouns the difference between endonym and ethnonym

is that endonym is a name used by a group or category of people to refer to themselves or their language, as opposed to a name given to them by other groups. For example, Deutsche is the endonym of a people known in English as German and Mapuche is the endonym for the people referred to by outsiders as Araucanos while ethnonym is the name of an ethnic group.