The Longest English Word "Pneumonoultramicroscopicsilicovolcanoconiosis"

Pneumonoultramicroscopicsilicovolcanoconiosis, which is a "disease of the lungs caused by inhalation of tiny particles of silica". Though this 45-letter word appears in several dictionaries, it is not a real word - it was invented in 1935 by Everett M. Smith to serve as the longest word ever to appear in an English language dictionary.