(American.) 1. A point where a stream or river disappears underground. The sinking water may filter through a choke that excludes cavers, or may flow into an open horizontal cave or vertical shaft, and while active all of these may be termed sinkholes. The flow of water may be very small, but in full flood many sinkholes swallow flows of tens of cubic meters per second. The character of sink water (or swallet water, as it is commonly termed by hydrologists), flowing directly and rapidly into an open cave, distinguishes it from percolation water [9]. 2. General terms for closed depressions. They may be basin, funnel, or cylindrical shaped [10]. See also closed depression; doline; ponor; stream sink; sumidero; swallet; swallow hole.