Mount Everesta is the singular genitive of Mount Everest.

Mount EverestN

Rare in texts

Norwegian Bokmål

Mount EverestNx

Nordsamisk-norsk ordbokdict-sme-nob/src/N_Propgeo_smenob.xml:29550Edit on GitHub Suggest

Case	Sg
Gen	Mount Everesta / Mount Everest
Ill	Mount Everestii
Loc	Mount Everestas