Supercalifragilisticexpialidocious (*breath*) is NOT the longest word in English.
This extra long word (that approximately means “fantastic”) was popularized by the movie Mary Poppins and was eventually added to the dictionary. What you probably didn’t know is that there is a word that is longer—yes longer—than this one. Pneumonoultramicroscopicsilicovolcanoconiosis is a type of lung disease caused by inhaling ash and dust. Go ahead and try pronouncing that!