Old English wægn "wheeled vehicle, wagon, cart," from Proto-Germanic *wagna, from PIE *wogh-no-, suffixed form of root *wegh- "to go, move, transport in a vehicle" (source also of Latin vehiculum). A doublet of wagon. Largely fallen from use by c. 1600, but kept alive by poets, who found it easier to rhyme on than wagon. As a name for the Big Dipper/Plough, it is from Old English (see Charles's Wain).
Old English Carles wægn, a star-group associated in medieval times with Charlemagne, but originally with the nearby bright star Arcturus, which is linked by folk etymology to Latin Arturus "Arthur." Which places the seven-star asterism at the crux of the legendary association (or confusion) of Arthur and Charlemagne. Evidence from Dutch (cited in Grimm, "Teutonic Mythology") suggests that it might originally have been Woden's wagon. More recent names for it are the Plough (by 15c., chiefly British) and the Dipper (1833, chiefly American).
It is called "the Wagon" in a Mesopotamian text from 1700 B.C.E., and it is mentioned in the Biblical Book of Job. The seven bright stars in the modern constellation Ursa Major have borne a dual identity in Western history at least since Homer's time, being seen as both a wagon and a bear: as in Latin plaustrum "freight-wagon, ox cart" and arctos "bear," both used of the seven-star pattern, as were equivalent Greek amaxa (Attic hamaxa) and arktos.
The identification with a wagon is easy to see, with four stars as the body and three as the pole. The identification with a bear is more difficult, as the figure has a tail longer than its body. As Allen writes, "The conformation of the seven stars in no way resembles the animal,--indeed the contrary ...." But he suggests the identification "may have arisen from Aristotle's idea that its prototype was the only creature that dared invade the frozen north." The seven stars never were below the horizon in the latitude of the Mediterranean in Homeric and classical times (though not today, due to precession of the equinoxes). See also arctic for the identification of the bear and the north in classical times.
A variety of French and English sources from the early colonial period independently note that many native North American tribes in the northeast had long seen the seven-star group as a bear tracked by three hunters (or a hunter and his two dogs).
Among the Teutonic peoples, it seems to have been only a wagon, not a bear. A 10c. Anglo-Saxon astronomy manual uses the Greek-derived Aretos, but mentions that "unlearned men" call it "Charles's Wain":
Arheton hatte an tungol on norð dæle, se haefð seofon steorran, & is for ði oþrum naman ge-hatan septemtrio, þone hatað læwede meon carles-wæn. ["Anglo-Saxon Manual of Astronomy"]
[Septemtrio, the seven oxen, was yet another Roman name.] The star picture was not surely identified as a bear in English before late 14c.
The unlearned of today are corrected that the seven stars are not the Great Bear but form only a part of that large constellation. But those who applied the name "Bear" apparently did so originally only to these seven stars, and from Homer's time down to Thales, "the Bear" meant just the seven stars. From Rome to Anglo-Saxon England to Arabia to India, ancient astronomy texts mention a supposed duplicate constellation to the northern bear in the Southern Hemisphere, never visible from the north. This perhaps is based on sailors' tales of the Southern Cross.
"four-wheeled vehicle to carry heavy loads," late 15c., from Middle Dutch wagen, waghen, from Proto-Germanic *wagna- (source also of Old English wægn, Modern English wain, Old Saxon and Old High German wagan, Old Norse vagn, Old Frisian wein, German Wagen), from PIE *wogh-no-, suffixed form of root *wegh- "to go, move, transport in a vehicle" (source also of Latin vehiculum). It is thus related to way.
In Dutch and German, it is the general word for "a wheel vehicle;" its use in English is a result of contact through Flemish immigration, Dutch trade, or the Continental wars. It has largely displaced the native cognate, wain. Spelling preference varied randomly between -g- and -gg- from mid-18c., until American English settled on the etymological wagon, while waggon remained common in Great Britain. Wagon-train is attested from 1810. Phrase on the wagon "abstaining from alcohol" is attested by 1904, originally on the water cart.
Proto-Indo-European root meaning "to go, move, transport in a vehicle."
The root wegh-, "to convey, especially by wheeled vehicle," is found in virtually every branch of Indo-European, including now Anatolian. The root, as well as other widely represented roots such as aks- and nobh-, attests to the presence of the wheel — and vehicles using it — at the time Proto-Indo-European was spoken. [Watkins, p. 96]
It forms all or part of: always; away; convection; convey; convex; convoy; deviate; devious; envoy; evection; earwig; foy; graywacke; impervious; invective; inveigh; invoice; Norway; obviate; obvious; ochlocracy; ogee; pervious; previous; provection; quadrivium; thalweg; trivia; trivial; trivium; vector; vehemence; vehement; vehicle; vex; via; viaduct; viatic; viaticum; vogue; voyage; wacke; wag; waggish; wagon; wain; wall-eyed; wave (n.); way; wee; weigh; weight; wey; wiggle.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vahati "carries, conveys," vahitram, vahanam "vessel, ship;" Avestan vazaiti "he leads, draws;" Greek okhos "carriage, chariot;" Latin vehere "to carry, convey," vehiculum "carriage, chariot;" Old Church Slavonic vesti "to carry, convey," vozŭ "carriage, chariot;" Russian povozka "small sled;" Lithuanian vežu, vežti "to carry, convey," važis "a small sled;" Old Irish fecht "campaign, journey," fen "carriage, cart;" Welsh gwain "carriage, cart;" Old English wegan "to carry;" Old Norse vegr, Old High German weg "way;" Middle Dutch wagen "wagon."
late 14c., as a type of diving bird, agent noun from dip (v.). As "a ladle or long-handled utensil for drawing liquid," from 1783, chiefly American English. Also "a Dunker, an Anabaptist" (1610s); "one who dips snuff" (1870). As the popular U.S. name for the asterism known in Britain as The Plough or Charles's Wain, attested by 1833, so called for the arrangement of the stars. Compare Big Dipper.
So called perhaps because the wood originally was used for wagon building and coachwork, but the sense evolution is not entirely clear. Meaning "panels lining the walls of rooms" is recorded from 1540s. Wainscoting is from 1570s.