What's the Longest Word in English
Yes, this article is about some of the longest English words on record. No, you will not find the very longest word in English in this article. That one word would span about fifty-seven pages. It's the chemical name for the titin protein found in humans. Its full name has 189,819 letters. Would you like to hear it pronounced? One man helpfully sounds it out in a YouTube video, but pop some popcorn before you get started! It will take you over three hours to watch—it's just slightly shorter than the film Gone with the Wind. Dictionaries omit the name of this protein and many other long words. Obviously, dictionaries have space constraints, and the average person would have no need to know the technical names of chemicals. Still, there are plenty of lengthy words in dictionaries. Let's take a moment to appreciate a few of them.
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1 Pneumonoultramicroscopicsilicovolcanoconiosis (forty-five letters) is lung disease caused by the inhalation of silica or quartz dust. 
2 Pseudopseudohypoparathyroidism (thirty letters) is a mild form of inherited pseudohypoparathyroidism that simulates the symptoms of the disorder but isn't associated with abnormal levels of calcium and phosphorus in the blood. 
3 Floccinaucinihilipilification (twenty-nine letters) is the estimation of something as valueless. Ironically, floccinaucinihilipilification is a pretty valueless word itself; it's almost never used except as an example of a long word. 
4 Antidisestablishmentarianism (twenty-eight letters) originally described opposition to the disestablishment of the Church of England, but now it may refer to any opposition to withdrawing government support of a particular church or religion. 
5 What's the longest word you know? If you watched Mary Poppins as a child, you might quickly think of supercalifragilisticexpialidocious (thirty-four letters). Mary Poppins described it as the word to use "when you have nothing to say." It appears in some (but not all) dictionaries. 
6 Incomprehensibilities set the record in the 1990s as the longest word "in common usage." How many times have you used this twenty-one-letter term? 
7 Strengths has only nine letters, but all except one of them are consonants! This earns the word a Guinness World Record. It is also one of the longest monosyllabic words of the English language. 
8 Euouae is six letters long, but all of the letters are vowels. It holds two Guinness World Records. It's the longest English word composed exclusively of vowels, and it has the most consecutive vowels of any word. If you are wondering about its meaning, it's a musical term from medieval times. 
9 and 10 Unimaginatively has lots of vowels—eight in total, if you count the final y. What's neat about this word is that its vowels and consonants alternate. It's not the longest word with alternating consonants and vowels, though. That position is held by honorificabilitudinitatibus, a twenty-seven-letter way of saying "with honorableness." 
11 If you tsktsk someone, you indicate your disapproval by the tsktsk sound or by some other means. Tsktsks is the longest word that doesn't contain a vowel. 
12 and 13 Isograms are words that do not repeat letters. The longest examples are uncopyrightable and subdermatoglyphic. An uncopyrightable song, for example, would not be eligible for copyright. This word has fifteen letters, but one other word without repeated letters is longer—subdermatoglyphic. It's seventeen letters, but you'll not have much opportunity to use it outside the realm of dermatology. 
14 The fourteenth word on our list describes the tendency to use long words—sesquipedalianism. If you possess this trait, you will enjoy trying to use the words in this article in your next conversation. If you are a true sesquipedalian, it shouldn't be too hard. Except, of course, for that 189,819-letter protein name . . . it's doubtful that your friends will wait three hours for you to finish saying it! 
What's the Longest Word in English
Source: https://www.grammarly.com/blog/14-of-the-longest-words-in-english/#:~:text=1%20Pneumonoultramicroscopicsilicovolcanoconiosis%20(forty%2Dfive%20letters,of%20silica%20or%20quartz%20dust.