[This list of the most commonly looked-up words at NYTimes.com is from 2009. We’ve since published the lists for 2010 and 2011 — don’t forget to check those out too. —Josh]

If The New York Times ever strikes you as an abstruse glut of antediluvian perorations, if the newspaper’s profligacy of neologisms and shibboleths ever set off apoplectic paroxysms in you, if it all seems a bit recondite, here’s a reason to be sanguine: The Times has great data on the words that send readers in search of a dictionary.

As you may know, highlighting a word or passage on the Times website calls up a question mark that users can click for a definition and other reference material. (Though the feature was recently improved, it remains a mild annoyance for myself and many others who nervously click and highlight text on webpages.) Anyway, it turns out the Times tracks usage of that feature, and yesterday, deputy news editor Philip Corbett, who oversees the Times style manual, offered reporters a fascinating glimpse into the 50 most frequently looked-up words on nytimes.com in 2009. We obtained the memo and accompanying chart, which offer a nice lesson in how news sites can improve their journalism by studying user behavior.

All of the 25-cent words I used in the lede of this post are on the list. The most confusing to readers, with 7,645 look-ups through May 26, is sui generis, the Latin term roughly meaning “unique” that’s frequently used in legal contexts. The most ironic word is laconic (#4), which means “concise.” The most curious is louche (#3), which means “dubious” or “shady” and, as Corbett observes in his memo, inexplicably found its way into the paper 27 times over 5 months. (A Nexis search reveals that the word is all over the arts pages, and Maureen Dowd is a repeat offender.)

Corbett also notes that some words, like pandemic (#24), appear on the list merely because they are used so often. Along those lines, feckless (#17) and fecklessness (#50) appear to be the favorite confounding words of Times opinion writers. The most looked-up word per instance of usage is saturnine (#5), which Dowd wielded to describe Dick Cheney’s policy on torture.

This is mostly just interesting — quiz: how many of these words can you define? — but it’s also a reminder that news sites are sitting on a wealth of data, from popular search terms to click rates, that can help them adjust to reader preferences. So are Times scribes being asked to rein in their vocabularies? That might be a Sisyphean (#37) task, but no, Corbett merely advised reporters to “avoid the temptation to display our erudition at the reader’s expense.”

After the jump, I’ve taken the original chart of 50 words, which was compiled by director of web analytics James Robinson, and run my own spreadsheet that also calculates look-ups per use. Below that, Corbett’s memo.

For comparison, here are the 25 most-frequently looked-up words on Dictionary.com over a few recent months. There’s no overlap.

And here’s the portion of Corbett’s memo concerning the list:

Big, Fancy Words

We know Times readers are a well-educated group. They expect sophisticated coverage and literate prose. They delight in good writing and don’t shy away from complicated topics.

On the other hand, they probably don’t carry an unabridged dictionary along with the newspaper as they take the subway to work. And they don’t expect a news article to pose the same linguistic challenge as “Finnegans Wake.”

Our choice of words should be thoughtful and precise, and we should never talk down to readers. But how often should even a Times reader come across a word like hagiography or antediluvian or peripatetic, especially before breakfast?

One benefit of reading The Times online is the “look up” function: double-click on any word and a little question mark appears. Click the question mark and you get a definition from the American Heritage Dictionary.

Our colleague James Robinson, the director of Web analytics, shared some intriguing data with me: a list of the words that had been looked up most often by Times readers so far this year.

Before you check out James’s list, a few words of caution. Don’t take the precise ranking or numbers too literally. Obviously, how often a word is looked up depends partly on how much it’s used and how many people are reading that article online. If Tom Friedman uses some moderately unusual word (say, fealty), and I use a real head-scratcher on the same day (say, phlogiston), it’s a good bet that more readers will look up his word.

And remember, I’m not suggesting that we should ban these or any challenging words. Some uses may be perfectly justified. But let’s keep in mind why we’re writing and who’s reading, and under what circumstances. And let’s avoid the temptation to display our erudition at the reader’s expense.

That said, here’s the list. Check it out, then return for a few final comments.

•••

I’ll admit that there were two words on the list that had me thoroughly stumped: sumptuary (“of or regulating expenses or expenditures; specif., seeking to regulate extravagance on religious or moral grounds”) and phlogiston (“an imaginary element formerly believed to cause combustion and to be given off by anything burning”).

Our handling of “phlogiston,” though, showed one way to help readers with a tricky word, even if they don’t click to look it up. It was in a quote in a Science story about physicists who work on Wall Street, and we gave the background before using the word:

But it is not so easy to get new ideas into the economic literature, many quants complain. J. Doyne Farmer, a physicist and professor at the Santa Fe Institute, and the founder and former chief scientist of the Prediction Company, said he was shocked when he started reading finance literature at how backward it was, comparing it to Middle-Ages theories of fire. “They were talking about phlogiston — not the right metaphor,” Dr. Farmer said.

•••

Some entries seem self-referential: it’s no coincidence that a list of obscure and difficult words includes abstruse and recondite, not to mention solipsistic. And while many of these words may look like a foreign language, some actually are: sui generis, bildungsroman and my old friend schadenfreude all make appearances. And some entries just seem baffling: how did we end up using louche 27 times?

•••

Remember, too, that striking and very specific words can become wan and devalued through overuse. Consider apotheosis, which we’ve somehow managed to use 18 times so far this year. It literally means “deification, transformation into a divinity.” An extended meaning is “a glorified ideal.” But in some of our uses it seems to suggest little more than “a pretty good example.” Most recently, we’ve said critics view the Clinton health-care plan as “the apotheosis of liberal, out-of-control bureaucracy-building,” and we’ve described cut-off shorts as “that apotheosis of laissez-faire wear.”

So what do we say if someone really is transformed into a god?