Bummer

The origin of this term, applied to Maj. Gen. William T. Sherman’s foragers during the March To The Sea and the Carolinas Campaign, is obscure but was common army parlance by 1864. Possibly deriving from the German Bummler, meaning “idler” or “wastrel,” the name was embraced by many soldiers, who believed it struck terror in the hearts of Southern people.
The soldiers of the Army of Georgia were authorized to live off the land, since it was Sherman’s intent to “make Georgia howl” and to lay just as heavy a hand on South Carolina, which many Federals considered a “hellhole of secession.” On the road from Atlanta to the sea and then north, Sherman’s columns left their supply bases far behind, and their wagons could not carry provisions sufficient for all. Nevertheless, the Union commander sought to regulate and limit foraging, keeping it within accepted rules of warfare. Each brigade leader was to organize a foraging detail under “discreet officers.” The details were empowered to gather rations and forage of any sort and quantity useful to their commands and could appropriate animals and conveyances without limit. Soldiers, however, were not to trespass on any private dwelling, were to avoid abusive or threatening language, and, when possible, were to leave each family “a reasonable portion [of provisions] for their maintenance.” In regions where the army moved unmolested, no destruction of property was permitted. But where bushwhackers or guerrillas impeded the march, corps commanders were enjoined to “enforce a devastation more or less relentless, according to the measure of hostility.”
Many who marched through Georgia and the Carolinas disregarded these prohibitions. Too often, foraging parties became bands of marauders answering to no authority. One conscientious bummer wrote to his sister about the depredations inflicted on South Carolina:

How would you like it, do you think, Ab, to have troops passing your house constantly … ransacking and plundering and carrying off everything that could be of any use to them? There is considerable excitement in foraging, but it is [a] disagreeable business in some respects to go into people’s houses and take their provisions and have the women begging and entreating you to leave a little when you are necessitated to take all. But I feel some degree of consolation in the knowledge I have that I never went beyond my duty to pillage.

Source: Historical Times Encyclopedia of the Civil War