Also especially British, plough.

Origin of plow

before 1100; Middle English plouh, plugh(e), plough(e), Old English plōh; cognate with German Pflug plow
Related formsplow·a·ble, adjectiveplow·a·bil·i·ty, nounplow·er, nouno·ver·plow, verbre·plow, verb (used with object), re·plowed, re·plow·ing.sub·plow, nounsub·plow, verbun·plow·a·ble, adjectiveun·plowed, adjectivewell-plowed, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for plow back

plow

noun, verb

the usual US spelling of plough
Derived Formsplower, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for plow back

plow

n.

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.

plow

v.

late 14c., from plow (n.). Transferred sense from 1580s. Related: Plowed; plowing.

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with plow back

plow back

Reinvest earnings or profits in one's business, as in This company plows back half its profits every year. This term transfers the farming practice of turning the soil from top to bottom to financial enterprises. [First half of 1900s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.