Definition of thalweg
1a : a line following the lowest part of a valley whether under water or not b : the line of continuous maximum descent from any point on a land surface or one crossing all contour lines at right angles c : subsurface water percolating beneath and in the same direction as a surface stream course
2 : the middle of the chief navigable channel of a waterway which constitutes a boundary line between states
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Origin and Etymology of thalweg
German talweg (formerly spelled thalweg), from tal valley (from Old High German) + weg way, path, from Old High German
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