Northern Sami language
The name of the island must be very old, from Proto-Norse "*Sai-aujo" ("sea-island"), and the Northern Sami language name "Sievju" is probably an old loan and reflection of this form. In Norse times the name was transformed first to "*Sæ-ey", and then to just "*Sei". The last element "land" means "land" or "island" is a later addition.