So what is the longest word in English?! Supercalifragilisticexpialidocious is NOT the longest word in English. This word was popularized by the movie Mary Poppins and was eventually added to the dictionary. Many people will think that this word is long enough but hey! Take a look at the next one. "Pneumonoultramicroscopicsilicovolcanoconiosis" I guess we all need to take a deep breathe after pronouncing this word. Pneumonoultramicroscopicsilicovolcanoconiosis is a type of lung disease caused by inhaling ash and dust. SO go ahead and try pronouncing the longest word in English!