1. A surface river or stream flowing onto or over karst that then disappears completely underground through a swallow hole (ponor) and which may or may not rise again and flow as a resurgent surface river or stream . 2. In a karst region, a surface stream that enters an underground course . Synonyms: (French.) perte de riviere; (German.) Flubversickerung, Flubchwinde; (Greek.) chanomenos potamos; (Russian.) iscezajuscaja reka; (Spanish.) rio sumente; (Turkish.) kayip nehir; (Yugoslavian.) ponornica, ponikalnica. See also ponornica; sinking stream. Compare intermittent river.