Words: thalweg [AHED]

thal·weg
PRONUNCIATION: tälvg
NOUN: Geology 1. The line defining the lowest points along the length of a river bed or valley. 2. A subterranean stream.
ETYMOLOGY: German : Tal, Thal, valley (from Middle High German tal, from Old High German) + Weg, way (from Middle High German wec, weg, from Old High German weg; see wegh- in Appendix I).