thalweg: [tahl-veg or tahl-veyk]
1. In geography and fluvial geomorphology:
a : A line following the lowest part of a valley whether under water (as in a river) or not. When underwater, the thalweg is
the longitudinal outline of a riverbed from source to mouth, measured from the deepest part of the river.b : The line of continuous maximum descent from any point on a land surface or one crossing all contour lines at right angles. c : Subterranean water flowing beneath and in the same direction as a surface stream course.
2. In international law:The middle of the chief navigable channel of a waterway which constitutes a boundary line between states
Origin: 1831. An English loan word from German. Thal
meaning "valley" and weg
meaning "way." In German, the modern spelling of the word is Talweg