In a Word: Pointing Out the Index

Managing editor and logophile Andy Hollandbeck reveals the sometimes surprising roots of common English words and phrases. Remember: Etymology tells us where a word comes from, but not what it means today.

When you see the word index, your thoughts probably go first to one of those alphabetical lists at the back of many nonfiction and reference books, the creation of which being what index cards were created for. You might, however, recall that the finger closest to your thumb is sometimes called your index finger; this is actually the older sense of the word, one that was lost and then found again.

The verb indicare — from in- “in, upon” and dicare “proclaim” — is Latin for “to point out.” That word would eventually become the English verb indicate. But it also, as a noun, became the Latin index, which could refer to practically anything that “points out,” in the sense of revealing or directing attention to something. It could be a sign, an informer, a discoverer, or, as I alluded to earlier, the forefinger — the digit most often used to point at things.

This type of index appears in late-14th-century English writing as a name for that first finger (or second, depending on how you count). At this time during the Middle English period, though, it was competing with the English name towcher — that is, “toucher,” because it’s the finger you use to touch things. Index lost that competition.

But it still found many uses in a more general “indicator” sense; for instance, the word was used to describe a hands on a clock. In 1559, under the authority of  Pope Pius IV, the Church published the Index Librorum Prohibitorum, often abbreviated simply to “the Index,” a list of books that Catholics were forbidden to read; that is, it was a book that pointed out which other books should not be touched. (They did this in part to suppress the spread of Protestant teachings.) In 1571, the Church also published the Index Expurgatorius, a list of books that shouldn’t be read unless certain passages were first removed, or expurgated.

So by the late 16th century, index had become a general term for an alphabetical list that organized the individual subjects of a book and pointed out where to find them.

The sense of the index being one’s pointer or touching finger had become obsolete, but later English speakers (and presumably Latin scholars of various levels) recognized the link between the Latin “thing that points out” and the literal “finger that points.” In the mid-18th century, Enlgish writings show that the “forefinger” sense was returning, though the digit was called the index finger, rather than just the index. (Rather like calling the thumb the thumb finger.)

Through the 19th century, index worked its way into the jargon of science (the refractive index), economics (stock indices), and computer science (SQL indexes). And still, of course, in publishing.