late Old English plog, ploh "plow; plowland" (a measure of land equal to what a yoke of oxen could plow in a day), possibly from a Scandinavian source (cf. Old Norse plogr "plow," Swedish and Danish plog), from Proto-Germanic *plogo- (cf. Old Saxon plog, Old Frisian ploch "plow," Middle Low German ploch, Middle Dutch ploech, Dutch ploeg, Old High German pfluog, German Pflug), a late word in Germanic, of uncertain origin. Old Church Slavonic plugu, Lithuanian plugas "plow" are Germanic loan-words, as probably is Latin plovus, plovum "plow," a word said by Pliny to be of Rhaetian origin.
Replaced Old English sulh, cognate with Latin sulcus "furrow." As a name for the star pattern also known as the Big Dipper or Charles's Wain, it is attested by early 15c., perhaps early 14c. The three "handle" stars (in the Dipper configuration) generally are seen as the team of oxen pulling the plow, though sometimes they are the handle.