Endonym
A name in the language of the people or place it names — Kernewek rather than Cornish.
The United Nations Group of Experts on Geographical Names defines an endonym as the “name of a geographical feature in an official or well-established language occurring in that area where the feature is situated” — Vārānasī rather than Benares, Aachen rather than Aix-la-Chapelle.
That definition is about places. This Atlas applies the same idea to languages, which is a conventional extension rather than the UNGEGN definition itself: an endonym is what a language is called by the people who speak it. Kernewek is the endonym; Cornish is what English calls it.
Where a profile knows the endonym, the Atlas gives it alongside the English name and draws the profile’s cover glyph from it, so the first mark on the page is written in the language’s own terms.