Supercalifragilisticexpialidocious. Surely this is the longest word in the English language, right? Wrong. So you say that it must be antidisestablishmentarianism? Wrong again. It is (warm up your tongue):

methionylglutaminylarginyltyrosylglutamylserylleucylphenylalanylalanylglutaminylleucyllysylglutamylarginyllysylglutamylglycylalanylphenylalanylvalylprolylphenylalanylyalylthreonylleucylglycylaspartylprolylglycylisoleucylglutamylglutaminylserylleucyllysylisoleucylaspartylthreonylleucylisoleucylglutamylalanylglycylalanylaspartylalanylleucylglutamylleucylglycylisoleucylprolylphenylalanylserylaspartylprolylleucylalanylaspartylglycylprolylthreonylisoleucylglutaminylasparaginylalanylthreonylleucylarginylalanylphenylalanylalanylalanylglycylvalylthreonylprolylalanylglutaminylcysteinylphenylalanylglutamylmethionylleucyalanylleucylisoleucylarginylglutaminyllysylhistidylprolylthreonylisoleucylprolylisoleucylglycylleucylleucylmethionyltyrosylalanylasparaginylleucylvalylphenylalanylasparaginyllysylglycylisoleucylaspartylglutamylphenylalanyltyrosylalanylglutaminylcysteinylglutamyllysylvalylglycylvalylaspartylserylvalylleucylvalylalanylaspartylvalylprolylvalylglutaminylglutamylserylalanylprolylphenylalanylarginylglutaminylalanylalanylleucylarginylhistidylasparaginylvalylalanylprolylisoleucylphenylalanylisoleucylcysteinylprolylprolylaspartylalanylaspartylaspartylaspartylleucylleucylarginylglutaminylisoleucylalanylseryltyrosylglycylarginylglycyltyrosylthreonyltyrosylleucylleucylserylarginylalanylglycylvalylthreonylglycylalanylglutamylasparaginylarginylalanylalanylleucylprolylleucylasparaginylhistidylleucylvalylalanyllysylleucyllysylglutamyltyrosylasparaginylalanylalanylprolylprolylleucylglutaminylglycylphenylalanylglycylisoleucylserylalanylprolylaspartylglutaminylvalyllysylalanylalanylisoleucylaspartylalanylglycylalanylalanylglycylalanylisoleucylserylglycylserylalanylisoleucylvalyllysylisoleucylisoleucylglutamylglutaminylhistidylasparaginylisoleucylglutamylprolylglutamyllysylmethionylleucylalanylalanylleucyllysylvalylphenylalanylvalylglutaminylprolylmethionyllysylalanylalanylthreonylarginylserine

Phew! What a mouthful! That was 1,913 letters long! It’s the chemical name for tryptophan synthetase A protein, as it appears in Mrs. Byrne's Dictionary of Unusual, Obscure and Preposterous Words.

Many attempts have been made to create the longest word in the English language. Some actually follow the grammatical and word formation rules of English (like anti…) while others just don’t (like super…). Anti… is actually a real word in real use, meaning one who opposes the disestablishment of the Church of England. Super… was popularized by the Walt Disney movie Mary Poppins, but has been found earlier, perhaps in the 1940’s. The word floccinaucinihilipilification was a joke word in the 18^th and 19^th Centuries. It stemmed from an Eton Grammar School Latin drill. These three words are the most often to be quoted as the longest in the English language, although, as you can see above, this is not the case any longer.

If you, however, are looking for a practical word that you can pronounce, but is actually a long word, try pneumonoultramicroscopicsilicovolcanokoniosis. This is the longest word (44 letters) listed in the Oxford English Dictionary, 2^nd ed.. But wait. Unfortunately, it turned out to be a hoax. It was coined by the 103^rd Session of the National Puzzler’s League at the Hotel New Yorker. Apparently, it is a factitious word supposedly referring to a lung disease caused by inhaling very fine silica dust. Coincidentally, it is often found in miners, according to the Scary Archive.

So you want a real word? Well, dichlorodiphenyltrichloroethane (DDT) fits the bill. It is longer than anti… and flocci…, and is a more serious word than super…. Plus, it’s very helpful to have a sesquipedalian word that is known more commonly by its TLA than by its full form. It is the longest word in the Macquarie Dictionary.

Tired yet? Yes? That’s understandable. If Shakespeare’s famous 26-letter word honorificabilitudintatibus (Love's Labour's Lost, Ⅴ.ⅰ.) got beat 73 times over as the longest word, you know that this had better be left to the experts. With that, impress your friends, and recite these ultimate tongue twisters to your teachers. Good luck!

[Update] By the way, the Guinness Book of World Records claims that the longest village sign in the world reads Llanfairpwllgwyngyllgogerychwyrndrobwilllantysiliogogogoch, which is Welsh for “The Church of Mary in the Hollow of the White Hazel near the Fierce Whirlpool and the Church of Tysilio by the Red Cave.”

[Update] This article is nothing compared to the very comprehensive Longest word in English article at Wikipedia, and many of the pages linked from there.