While it's definitely a long word, there are many longer words in the English language, including:
* Pneumonoultramicroscopicsilicovolcanoconiosis: A lung disease caused by inhaling very fine silica dust.
* Floccinaucinihilipilification: The act of estimating something as worthless.
* Antidisestablishmentarianism: Opposition to the separation of church and state.
There are also some very long technical terms used in scientific fields.
So, while "supercalifragilisticexpialidocious" is a fun and memorable long word, it's not the longest one out there!