One question I often field in my capacity as OUP’s editor for American dictionaries is, “What’s the longest word in the dictionary?” I don’t hear it as often as “How do I get a new word in the dictionary?” but it still comes up from time to time. My stock answer isn’t very interesting: “It depends on what counts as a ‘word,’ and it depends on the dictionary.” That answer doesn’t satisfy most people, since the follow-up question is typically something like, “No, really, is it antidisestablishmentarianism or supercalifragilisticexpialidocious?” Those two specimens are the “usual suspects” that get hauled out in discussions of the longest word in English, perhaps because most of us have been familiar with them since grade school. But there are many other worthy candidates for the “longest word” mantle.First, some ground rules. Let’s say that a “word” is a single lexical item that is unbroken by spaces or hyphens. That’s a rather arbitrary distinction, but it accords with most people’s judgments of wordhood. (When the New Oxford American Dictionary named carbon neutral the 2006 Word of the Year, there were numerous complaints that this is actually two words. But as Oxford English Dictionary editor at large Jesse Sheidlower pointed out in another context, promoting the “Lexical Item of the Year” doesn’t have quite the same ring to it.) By those standards, the longest word that has entered any major English dictionary is this 45-letter whopper: pneumonoultramicroscopicsilicovolcanoconiosis, meaning ‘a lung disease caused by inhaling very fine ash and sand dust.’ You can find it under the prefix pneumono- in the online edition of the Oxford English Dictionary, as well as the Shorter Oxford English Dictionary.There’s only one problem with P45, as it’s known to its friends: it’s most likely a fabrication. As described in an article in the magazine Word Ways, the word appears to have been invented on the occasion of a 1935 meeting of the National Puzzlers League in New York. The NPL’s president at the time, Everett M. Smith, presented it as “the longest word in the English language.” But there’s not a shred of evidence that the word was used in medical literature before Smith unveiled it at the NPL meeting and the press picked up on the fanciful story. It looks like Smith simply made it up. Indeed, both the OED and the Shorter OED now warn readers that P45 is factitious, occurring only as an example of an ultra-long word.And that’s the problem with many of the “longest word” candidates: you only ever encounter them in discussions of very long words. The 33-letter word in the title of this post, hippopotomonstrosesquipedalianism, is even more self-referential, since it’s used to describe words that are enormously long (or sesquipedalian, literally ‘a foot and a half long’).You won’t find that in any dictionary, since it’s nothing more than a flashy “stunt word.” Then again, P45 started its life as a stunt word and then managed to find its way into dictionaries, so you never know. Supercalifragilisticexpialidocious (34 letters) was a stunt word too, specifically created for a song in Mary Poppins, but the film version of the musical was popular enough that everyone got to know the word. Now it’s in a number of dictionaries, including the OED.A stunt word with a more distinguished pedigree is the 29-letter floccinaucinihilipilification, ‘the action or habit of estimating as worthless,’ dating back to 1741. This strings together a sequence of Latin words that were taught at Eton College: flocci, nauci, nihili, pili (meaning ‘at little value’), with the -fication suffix tacked on. This is the longest word in NOAD, the Concise OED, and many other dictionaries. It’s an obsolete word and has never been more than a lexical curiosity, but politicians seem to enjoy trying to revive it: the US senators Robert Byrd, Daniel Patrick Moynihan, and Jesse Helms have all included it in their oratory. Antidisestablishmentarianism, at 28 letters (’opposition to the disestablishment of the Church of England’) has at least been used historically in less self-conscious contexts, but it too has become limited to simply yet another example of a very long word.So how about words that people actually use in normal speech? A common 20-letter word is uncharacteristically, and another one is internationalization (handily called “i18n” by some to avoid spelling out the 18 letters in the middle). And there are even a few words of 22 letters in length that aren’t too ostentatious: deinstitutionalization, counterrevolutionaries, and electroencephalography. Once you get beyond the 22-letter limit, though, most long words are ones you wouldn’t encounter outside of scientific literature. Very often they’re words for chemical compounds that iconically represent the structure that they name. If they’re known to a popular audience at all, they’re given shorthand labels. So we know tetrachlorodibenzoparadioxin (28 letters) as TCDD or dioxin, methylenedioxymethamphetamine (29 letters) as MDMA or ecstasy, and dichlorodiphenyltrichloroethane (31 letters) as DDT.Biochemists can give extravagantly long names to enzymes, lipids, and the like, since the words are formed by stringing together elements representing chains of acids. That doesn’t mean the scientists will actually use these words very often, though. Looking through the Oxford English Corpus for long words, I found a 39-letter word that does seem to be used regularly in scientific literature: it’s palmitoyloleoylphosphatidylethanolamine, a lipid known more succinctly as POPE. I hereby declare this specimen to be the POPE of outrageously long words.