Pneumonoultramicroscopicsilicovolcanoconiosis (/ˌnjuːmənoʊˌʌltrəˌmaɪkrəˈskɒpɪkˌsɪlɪkoʊvɒlˌkeɪnoʊˌkoʊniˈoʊsɪs/ ⓘ[1][2]) is a 45-letter word coined in 1935 by the then-president of the National Puzzlers' League, Everett M. Smith.
It is the longest word in the English language published in a popular dictionary, Oxford Dictionaries, which defines it as "an artificial long word said to mean a lung disease caused by inhaling very fine ash and sand dust".
The word featured in the headline for an article published by the New York Herald Tribune on February 23, 1935, titled "Puzzlers Open 103rd Session Here by Recognizing 45-Letter Word":[6] 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 synonym of a special form of pneumoconiosis caused by ultra-microscopic particles of silica volcanic dust...Although it has been defined as an extension of pneumoconiosis, there is no scientific evidence for a similar disease related to volcanic silica particle exposures.
[8] Subsequently, the word was used in Frank Scully's puzzle book Bedside Manna, after which time, members of the N.P.L.