1. Depression revealing a part of a subterranean river flowing across its floor, or an unroofed part of a cave. 2. A small natural bridge or arch which can be seen through [10]. 3. A through opening in natural limestone walls, formed by the joining of karst grottos as a result of dissolution processes [20]. Synonyms: (French.) fenetre karstique; (German.) Karstfenster; (Greek.) karstikon parathyron; (Italian.) finestra carsica; (Russian.) karstovoe okno; (Spanish.) dolina en ventana; (Turkish.) karst penceresi; (Yugoslavian.) krsko (krasko) okno.