gorosti.

Possibly from Proto-Basque *golosti, but the ultimate origin is unknown. Perhaps a Mediterranean Wanderwort also found in Sardinian golosti, colostri (“holly”) and Ancient Greek κήλαστρος (kḗlastros, “holly”). Beyond Sardinian and Greek, which clearly bear some resemblance to Basque, other putative cognates have been proposed. Some authors also cite Ticinese ğüštrún, šištrún (“whortleberry, Vaccinium myrtillus”), apparently from Proto-Celtic *glastos (“green”), via Gallo-Italic *wolostrone, but the semantics is quite doubtful. Agud and Tovar (1994) note that Old English gorst, English gorse (“furze, bramble”) and German Gerste (“barley”) are similar in shape to this word, however, as the Celtic term, they have a well-established Indo-European etymology. Derivations that try to explain this word as a Basque compound, such as gora (“up, above”) + osto (“leaf”), or that link it to garratz (“sour”) are to be considered folk etymologies.