Where did the word supercalafragalisticexpialadoshus come from?

The word "supercalifragilisticexpialidocious" is a made-up word, invented specifically for the 1964 musical film "Mary Poppins." It was created by the film's songwriters, the Sherman brothers, as a nonsensical word that sounds impressive and whimsical.

There's no real etymology or origin for the word, it's purely a fabrication. It became popular due to its use in the film and the catchy song "Supercalifragilisticexpialidocious."