pneumonoultramicroscopicsilicovolcanoconiosis

'''''''''' ( ) is a 45-letter word coined in 1935 by Everett M. Smith, the then-president of the National Puzzlers' League. It has sometimes been used as a synonym for the occupational disease known as silicosis; however, this term is incorrect, as most silicosis is not related to mining of volcanic dusts. Silicosis is a form of occupational lung disease caused by inhalation of 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. Pneumonoultramicroscopicsilicovolcanoconiosis 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".

Clinical and toxicological research conducted on volcanic crystalline silica has found little to no evidence of its ability to cause silicosis/-like diseases and geochemical analyses have shown that there are inherent factors in the crystalline structure which may render volcanic crystalline silica much less pathogenic than some other forms of crystalline silica.