Q: Why does “biscuit,” which literally means “baked twice,” refer to food that, in most instances, is not baked twice?
A: When the word “biscuit” showed up in English in the Middle Ages (spelled “besquite”), it did indeed refer to food that was baked twice.
The Oxford English Dictionary says the word is derived “from the original mode of preparation.” The ultimate source of the word, according to the OED, is “the Latin biscoctum (panem), bread ‘twice baked.’ ”
In the original method of cooking, John Ayto explains in his Dictionary of Word Origins, the biscuits were “returned to the oven after the initial period of baking in order to become dry or crisp.”
When the term first appeared in Middle English writing in the 14th century, according to Merriam-Webster Unabridged, it referred to “hard or crisp dry baked products” (similar to what Americans today would call a “cracker” or “cookie,” and the British a “biscuit”). In the US, a “biscuit” is a quick bread leavened with baking powder or baking soda.
The British cooking writer Elizabeth David has suggested that the American use of “biscuit” may have been influenced by a similar usage in Scotland and Guernsey, where the term can refer to soft biscuits like scones. It may be that Scottish immigrants brought the usage to America.
“It is interesting that these soft biscuits (such as scones) are common to Scotland and Guernsey, and that the term biscuit as applied to a soft product was retained in these places, and in America, whereas in England it has completely died out,” she writes in English Bread and Yeast Cookery (1977).
The earliest example of “biscuit” in the OED is from a chronicle written around 1330 by the English monk Robert Mannyng: “Armour þei had plente, & god besquite to mete” (“They had plenty of armor and weapons, and biscuits for good measure”).
The first Oxford example of “biscuit” used in the American sense of a quick cake is from John Palmer’s Journal of Travels in the United States of North America and Lower Canada (1818): “Hot short cakes, called biscuits.”
Interestingly, the “biscuit” spelling is the result of the Frenchification of “bisket,” which was the standard English spelling for hundreds of years.
As the OED explains, “The regular form in English from 16th to 18th cents. was bisket, as still pronounced; the current biscuit is a senseless adoption of the modern French spelling, without the French pronunciation.”
[Update, Feb. 13, 2018: A reader points out that the German term zwieback literally means twice-baked, from zwei (“two”) and backen (“to bake”). And the Italian biscotti has a similar meaning.]