Is it ensure, insure, or assure?
"strong drink, drink laced with chloral hydrate," by 1928 (perhaps 1890s), of unknown origin. Presumably named after someone, but the various stories about the name cannot be substantiated.
[origin unknown and richly conjectured, chiefly being fathered on various bartenders or saloon proprietors with names like Mickey Finn]
[potato sense probably by association with the common phrase Irish potato]