Pneumonoultramicroscopicsilicovolcanoconiosis
Pneumonoultramicroscopicsilicovolcanoconiosis (/ˌnjuːmənoʊˌʌltrəˌmaɪkrəˈskɒpɪkˌsɪlɪkoʊvɒlˌkeɪnoʊˌkoʊniˈoʊsɪs/ (listen)) 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, the Oxford English Dictionary, which defines it as "an artificial long word said to mean a lung disease caused by inhaling very fine ash and sand dust".
Pneumonoultramicroscopicsilicovolcanoconiosis-1