How do you spell supercalifragilisticespiolodocous?

You're thinking of supercalifragilisticexpialidocious, a word from the movie "Mary Poppins."

There's no such word as "supercalifragilisticespiolodocous." It's a fun play on words combining "supercalifragilisticexpialidocious" and "Diplodocus", a dinosaur.