What Is the Longest Word in English?

longest word Tatiana Ayazo/rd.com

There are about a million words in the English language, but do you know the longest word in English? You may think it’s antidisestablishmentarianism, at 28 letters long. Or is it hippopotomonstrosesquippedaliophobia? Nope. At 36 letters, hippo… is no match for pneumonoultramicroscopicsilicovolcanoconiosis, which clocks in at a whopping 45 letters long (and try saying it three times fast!).

While those are all strong (and long) guesses, the longest word in the English language is methionylalanylthreonylserylarginylglycylalanylserylarginylcysteinylprolylarginylaspartylisoleucylalanylasparaginylvalylmethionylglutaminylarginylleucylglutaminylaspartylglutamylglutaminylglutamylisoleucylvalylglutaminyllysylarginylthreonylphenylalanylthreonyllysyltryptophyl … and that’s not even a fraction of the entire word. The full, technical name of this protein, better known as titin—a folded, spring-like protein that helps keep our muscles elastic—has a total letter count of 189,819. For perspective, the most complicated word in English comes in at just three letters long, though it has a whopping 645 meanings.

Keep reading, and we’ll get into the lengthy details.

What does the longest word in English mean?

If you don’t think this monstrous moniker should be considered a real English word, you’d find some support from linguists. As a technical scientific term, the full name of titin doesn’t appear in any dictionary—not just because it would take 12 full pages to wrangle the nearly 190,000 characters, but because of the way protein names are generated. According to international guidelines, a protein’s technical title lists every single amino acid found inside it. Even the smallest proteins contain no fewer than 20 amino acids, making for some pretty long names. Titin, however, is the human body’s largest protein. Total amino acid count: 34,350. Spell out each of those acid names in a row and you get, well, a really long word. (You can probably see why scientists prefer titin.)

Other long words and their definitions

So if dictionary editors don’t choose to fill their pages with titin’s full name, what is the longest word in the dictionary? That depends on which dictionary you consult. A few contenders:

The longest word in the Oxford English Dictionary is 45 letters: pneumonoultramicroscopicsilicovolcanoconiosis. According to the OED, this synonym for silicosis was coined in the 1930s as a jab at overly complicated medical terms. Yep, the longest word in the dictionary is a joke.
The longest well-known nonsense word is 34 letters: supercalifragilisticexpialidocious. Anyone versed in Mary Poppins can define this for themselves, but according to Oxford the fanciful adjective means “extraordinarily good.”
The longest word that’s also the most ironic:
hippopotomonstrosesquippedaliophobia. This is a term for a fear of long words, though it’s not a phobia officially recognized by the American Psychiatric Association.
The longest non-coined, non-technical word published in multiple dictionaries is 28 letters long: antidisestablishmentarianism. Even Merriam-Webster refuses to include it in their pages due to a lack of long-term use. What does it actually mean? It used to refer to a 19th-century political party opposed to the disestablishment of the Church of England—but today it mainly means “I know a really long word.”

Debate rages among word nerds as to which of these is truly the longest word in English. When it comes to our constantly evolving language, your opinion is as valid as anyone’s.

Zoom out, and the North Island of New Zealand holds the world record for the longest place name, at 85 letters: Taumatawhakatangihangakoauauotamateaturipukakapikimaungahoronukupokaiwhenuakitanatahu. Locals call it Taumata or Taumata Hill.

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