What is the longest word in English?

Surely it's the 'longest word you ever heard' - all together now: 
 
The word was invented by the Sherman brothers for the musical. According to some  learned sources, the word has some very fancy linguistic roots:
super- "above", cali- "beauty", fragilistic- "delicate", expiali- "to atone", and docious- "educable", with the sum of these parts signifying roughly "Atoning for educability through delicate beauty." Although the word contains recognizable English morphemes, it does not follow the rules of English morphology as a whole ....
More fun to know is that the working relationship of the Sherman brothers was not 'practically perfect'. When Disney Studio drafted them in to save the score of Mary Poppins 'creative differences' ended with them throwing typewriters at each other.

A version of this post is included in 50 FAQ about English  ($1.75)