cabbage (n.)

"a polished but uncut precious stone," 1570s, from French cabochon (14c.), augmentative of caboche (12c.), itself an augmentative or pejorative formation, ultimately from Latin caput "head" (from PIE root *kaput- "head"). Essentially the same word as cabbage.

1762, said to be a reference to John Montagu (1718-1792), 4th Earl of Sandwich, who was said to be an inveterate gambler who ate thin slices of cold meat between bread at the gaming table during marathon sessions rather than rising for a proper meal (this account of the origin dates to 1770). By 1762 these sandwiches were being served in upscale dining clubs. The open faced sandwich, served on a single slice of bread, is recorded by 1920.

SANDWICHES. — Two small slices of bread and butter, almost transparent, with a thin piece of stale ham, or beef, between them, and used to keep the people in the gallery from famishing from Eleven o'clock, till six the next morning.—N. B. Bellamy charges a shilling for them, and they don't stand him in above two pence. ["Pearson's Political Dictionary," 1792]

It also was in his honor that Cook named the Hawaiian islands (1778) when Montagu was first lord of the Admiralty (hence the occasional 19c. British Sandwicher for "a Hawaiian"). The family name is from the place in Kent, one of the Cinque Ports, Old English Sandwicæ, literally "sandy harbor (or trading center)." For pronunciation, see cabbage. Sandwich board, one before and one behind the carrier, is from 1864.