The longest word in the English language, according to the Oxford English Dictionary, is pneumonoultramicroscopicsilicovolcanoconiosis, a lung disease caused by inhaling silica particles. This word was coined by Everett M. Smith, the president of the National Puzzlers' League, in 1935. It has 45 letters and is considered the longest English word by the Oxford English Dictionary and the Guinness Book of World Records. Despite its length, the word is rarely used in medical literature.