Tarn, Thalweg, Torrent: Origins, Forms, Histories of Words Meaning River, Lake

The natural features of a region are its topography (Greek topos, "place"). Topographic features include rivers, lakes, and similar freshwater bodies.

Freshwater features have accumulated a wide range of colorful names. In the current alphabetic series of words that refer to such features, here are the origins, forms, and histories of tarn, thalweg, and torrent. The dates of forms and meanings come from the Oxford English Dictionary and Merriam-Webster's Collegiate Dictionary.

Tarn
Modern English tarn (17th century) comes from Middle English tarne (15th century) and terne (14th century). The word is of Scandinavian origin and is akin to Old Norse tjorn ("small lake").

A small, steep-banked mountain lake or pool is a tarn (14th century). The word originated in the dialects of northern England (where many Scandinavians settled), but it long ago attained general usage in English.

Thalweg
Thalweg entered English in the 19th century from German Thalweg ("bottom path of a valley"), from thal ("valley") and weg ("way, path"). Both elements of the word come from Old High German. While thalweg remains the standard spelling in English, the German word is now spelled Talweg.

The original meaning of thalweg is a line following the lowest part of a valley and forming a natural watercourse, whether actually under water or not (1862). From that sense has come the following extensions: a line following the deepest part of the channel of any river or lake; subsurface water percolating beneath, and in the same direction as, a surface stream; and the middle of the chief navigable channel of a waterway that constitutes a boundary line between states.

Torrent
Torrent entered English in the 16th century from Middle French torrent, from Latin torrent-, a combining form of torrens, from the adjective torrent-, torrens ("burning, seething, rushing"), from the present participle of torrere ("to torch, burn").

A stream of water flowing with great speed and force, whether from the steepness of its channel or from the pressure of flooding, is known as a torrent (16th century). The word is especially applied to a mountain stream that is at times full of running water and at other times dry or nearly dry.
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Encyclopaedia Britannica Ready Reference 2004. CD-ROM. Encyclopaedia Britannica, 2004.

Merriam-Webster's Collegiate Dictionary. 11th ed. Springfield, Mass.: Merriam-Webster, 2006.

Merriam-Webster's Geographical Dictionary. 3rd ed. Springfield, Mass.: Merriam-Webster, 2007.

The Oxford English Dictionary. 2nd ed. Oxford, England: Clarendon Press, 1989.