Trench, Trough, Tube, Tunnel, Underground: Origins, Forms, Histories of Words Meaning Valley, Cave

The natural features of a region are its topography (Greek topos, "place"). Most topographic features have acquired a wide range of names to stand for the same or similar entities.

Valleys and caves, for example, as well as related natural forms and human-made structures, are known by many words in English. In the current alphabetic series of such terms, the next examples are trench, trough, tube, tunnel, and underground.

Trench
Modern English trench comes from Middle English trench (14th century) and trenche (14th century), from Middle French trenche ("act of cutting"), from trenchier ("to cut"), probably from (assumed) Vulgar Latin trinicare ("to cut in three"), from Latin trini ("three each").

The original, now obsolete, meaning of trench is a path or track cut through woods (14th century).

Transferred to the earth, trench means a long hollow cut out of the ground, especially one used for military defense (15th century).

Trough
Modern English trough comes from Middle English trough (15th century), from Old English trog (before 12th century). The word is akin to Old High German trog ("trough") and Old English treow ("tree, wood").

The original meaning of trough is a long shallow receptacle, often made of wood, to hold the feed and water of domestic animals (8th century).

A natural feature that resembles a trough by being long and narrow or shallow is a trough (1513). Examples include a valley or hollow between hills, a long but shallow depression in the bed of the sea, and the bed or channel of a stream.

Tube
Tube entered English in the 17th century from French tube, from Latin tubus. The word is akin to Latin tuba ("trumpet").

Any of various cylindrical objects is a tube (17th century).

The cylindrical tunnel in which an underground electric railway runs is called a tube (1900) in British English. In the United States, the tunnel is called a subway.

Tunnel
Modern English tunnel (16th century) comes from Middle English tonel (15th century), from Middle French tonel ("tun"), from Old French tonel ("tun"), from tonne ("tun"), from Medieval Latin tunna ("tun").

The original meaning of tunnel is a tun-shaped (that is, cask-shaped or pipe-shaped) net for catching birds, especially waterfowl (15th century). The word soon extended to include various kinds of hollow conduits, such as a funnel or the flue of a chimney (16th century).

A subterranean gallery in a mine or a cave, a roadway excavated underground (as for a railway), or a covered passageway through or under an obstruction is a tunnel (18th century). An animal burrow is also called a tunnel (19th century).

Underground
The noun underground emerged in the late 16th century from the slightly earlier use of the word as an adverb meaning "below the surface of the ground" (1571).

Any subterranean space or channel is an underground (1594).

An underground railway system, including the passage, or tunnel, through which the tracks run, is called an underground or an underground railway (both 19th century).
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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.