Pneumonoultramicroscopicsilicovolcanoconiosis

Pneumonoultramicroscopicsilicovolcanoconiosis is a 45-letter word coined in 1935 by Everett M. Smith, then president of the National Puzzlers' League, and it is the longest word in the English language to appear 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 has sometimes been used as a synonym for the occupational disease silicosis, but that usage is incorrect, because most silicosis is not caused by inhaling volcanic dust. Silicosis itself is an occupational lung disease caused by breathing crystalline silica dust and is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis. Clinical and toxicological research on volcanic crystalline silica has found little or no evidence that it causes silicosis-like disease, and geochemical analyses suggest that features of its crystal structure may make it much less harmful than other forms of crystalline silica.