from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Geology The line defining the lowest points along the length of a river bed or valley.
- n. Geology A subterranean stream.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The line that connects the lowest points in a valley or river channel, and thus the line of fastest flow along a river’s course.
from the GNU version of the Collaborative International Dictionary of English
- n. A line following the lowest part of a valley, whether under water or not.
- n. The line of continuous maximum descent from any point on a land surface, or that cutting all contours and angles.
from The Century Dictionary and Cyclopedia
- n. A line upon a topographical surface which is a natural watercourse, having everywhere the direction of greatest slope, and distinguished by having the lines of straight horizontal projection which cut it at right angles on the upper sides of the curves of equal elevation to which they are tangent.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the middle of the chief navigable channel of a waterway that forms the boundary line between states
- n. a line following the lowest points of a valley
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).(American Heritage® Dictionary of the English Language, Fourth Edition)
From 19th century German Thal ("valley") + Weg ("way, course") (Wiktionary)