Pneumonoultramicroscopicsilicovolcanoconiosis is, according to the Oxford English Dictionary, "a factitious word alleged to mean 'a lung disease caused by the inhalation of very fine silica dust, causing inflammation in the lungs.'" A condition meeting the word's definition is normally called silicosis.
It occurs chiefly as an instance of a very long word. The 45-letter word was coined to serve as the longest English word and is the longest word ever to appear in an English language dictionary. It is listed in the current edition of several dictionaries.
This word was invented in 1935 by Everett M. Smith, president of the National Puzzlers' League, at its annual meeting. The word figured in the headline for an article published by the New York Herald Tribune on February 23, 1935, titled "Puzzlers Open 103d Session Here by Recognizing 45-Letter Word":
Pneumonoultramicroscopicsilicovolcanoconiosis succeeded electrophotomicrographically as the longest word in the English language recognized by the National Puzzlers' League at the opening session of the organization's 103rd semi-annual meeting held yesterday at the Hotel New Yorker. The puzzlers explained that the forty-five-letter word is the name of a special form of silicosis caused by ultra-microscopic particles of silica volcanic dust...
Subsequently, the word was used in a puzzle book, Bedside Manna, after which members of the NPL campaigned to have it included in major dictionaries.
Cultural references 
- In a 1965 episode of I've Got a Secret, Buddy Hackett unrolls a banner with the word on it and has the panel try to pronounce it.
- "Floccinaucinihilipilification," the second of Irish composer David Flynn's "Two Nonsense Songs," ends with the word sung in a mock operatic cadenza style.
- The word often appears in books or stories as a comically long word, e.g. "Grampa vs. Sexual Inadequacy" (an episode of The Simpsons), Abraham Simpson asks Homer whether pneumonoultramicroscopicsilicovolcanoconiosis is what's wrong with Marge; a cartoon episode of Rocket Power, in which a dimwitted character named Twister successfully spells the word on his spelling test; High School Musical 2: What's What Edition refers to this as the longest word.
See also 
|Look up pneumono... in Wiktionary, the free dictionary.|
- Longest word in English
- Oxford English Dictionary; Pneumonoultramicroscopicsilicovolcanoconiosis definition in the Oxford English Dictionary
- Oxford English Dictionary online, Oxford University Press, quote listed in "Second Edition 1989" definition. "Draft revision Sept. 2006" definition reads "a word invented (prob. by Everett M. Smith (born 1894), president of the National Puzzlers' League in 1935) in imitation of polysyllabic medical terms, alleged to mean 'a lung disease caused by the inhalation of very fine sand and ash dust' but occurring only as an instance of a very long word." Retrieved on 2007-10-08.
- "Pneumonoultramicroscopicsilicovolcanoconiosis: Definitions from dictionary.com". Dictionary.com. Retrieved on 2007-10-09.
- Cole, Chris (1999). Wordplay, A Curious Dictionary of Language Oddities. Sterling Publishing Co., Inc. pp. 106–107. ISBN 0-8069-1797-0.
- Cole, Chris. (1989.) "The Biggest Hoax". Word Ways: The Journal of Recreational Linguistics, via wordways.com. Retrieved on 2007-10-08.
- Miller, Jeff. "A collection of word oddities and trivia: page 11, long words". (Personal website.) Retrieved on 2007-10-08.
- tWO nONSENSE sONGS, Contemporary Music Centre, Ireland: Library. Retrieved 2010-07-20.