"Supercalifragilisticexpialidocious" is a long word that was invented simply to be a long word. Its meaning is incidental. Nonetheless, it appears in some dictionaries. Wordsmith.org defines it as:
A nonsense-word used esp. by children, now chiefly expressing excited approbation: fantastic, fabulous.
(Or in other words, the last 29 letters are essentially superfluous.)
Most of us know this quite atrocious-sounding word from the song of the same name, which featured prominently in the 1964 Disney classic Mary Poppins. I always assumed that this was how "supercali..." was introduced into the English lexicon, and that Disney's fantastic songwriters Richard and Robert Sherman coined the word themselves. But it turns out that's only true for this specific spelling of the word.
The "supercali..." phenom
was not a
So where did The Word come from in the first place? It's still a mystery. While it seems pretty clear that The Word was made up by someone — probably a kid — with the specific intention of creating "the longest word ever," there's no written documentation of its origin. Rumours persist that 19th century Scottish miners used the word to give "orders" to prostitutes, but that's almost certainly poppycock.
The
Sources: Wordsmith.org, The Straight Dope, The Phrase Finder