Longest word in English

The identity of the longest word in English depends upon the definition of what constitutes a word in the English language, as well as how length should be compared. In addition to words derived naturally from the language's roots (without any known intentional invention), English allows new words to be formed by coinage and construction; place names may be considered words; technical terms may be arbitrarily long. Length may be understood in terms of orthography and number of written letters, or (less commonly) phonology and the number of phonemes.

The longest word in any of the major English language dictionaries is pneumonoultramicroscopicsilicovolcanoconiosis, a word that refers to a lung disease contracted from the inhalation of very fine silica particles, specifically from a volcano; medically, it is the same as silicosis. The word was deliberately coined to be the longest word in English, and has since been used in a close approximation of its originally intended meaning, lending at least some degree of validity to its claim.

The Oxford English Dictionary contains pseudopseudohypoparathyroidism (30 letters).

Merriam-Webster's Collegiate Dictionary does not contain antidisestablishmentarianism (28 letters), as the editors found no widespread, sustained usage of the word in its original meaning. The longest word in that dictionary is (27 letters).

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