That word comes from a movie called "Mary Poppins".
This is the part that people usually remember:
Supercalifragilisticexpialidocious!
Even though the sound of it is something quite atrocious
If you say it loud enough, you’ll always sound precocious
Supercalifragilisticexpialidocious!Much of the scene in the movie actually centers on the fact that it's a made-up word which is neither easy to say nor to remember.
As I recall, they also manage to say it backwards, too (
suoicodiliaipxecitsiligarfilacrepus).

Here is a link:
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