Invented in the 1960s as the name of a can of food bulging at both ends because of an accumulation of gases caused by spoilage (therefore making the item eligible for a discount), the noun sweller ultimately derives from an Indo-European source that made its way into dozens of languages including—of course—Medieval Gothic where it appeared as ufswalleins, meaning the state or condition of being puffed up. The term flipper, incidentally, refers to a can of food bulging at only one end; the name derives from how the bulge, if pressed, will “flip” to the other end of the can.