pneumonoultramicroscopicsilicovolcanoconiosis

noun

pneu·​mo·​no·​ul·​tra·​mi·​cro·​scop·​ic·​sil·​i·​co·​vol·​ca·​no·​co·​ni·​o·​sis ˈn(y)ü-mə-(ˌ)nō-ˌəl-trə-ˌmī-krə-ˈskäp-ik-ˈsil-i-(ˌ)kō-väl-ˈkā-nō-ˌkō-nē-ˈō-səs 

plural pneumonoultramicroscopicsilicovolcanoconioses -ˌsēz 

: a pneumoconiosis caused by inhalation of very fine silicate or quartz dust