Pneumonoultramicroscopicsilicovolcanoconiosis is a word coined by the president of the National Puzzlers' League as a synonym for the disease known as silicosis? It is the longest word in the English language published in a 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"

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

Pneumoconiosis is the general term for a class of interstitial lung diseases where inhalation of dust has caused interstitial fibrosis

Silicosis is a form of occupational lung disease caused by the inhalation of crystalline silica dust.

More Info: en.wikipedia.org