wain (n.)

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).