It was introduced into the Mary Poppins story by American composers Robert and Richard Sherman when they adapted the PL Travers book for the big screen.
In the 1964 musical film, starring Julie Andrews, the nanny with magical powers wins an unorthodox race - on merry-go-round horses - and is surrounded by reporters who say she must be lost for words.
In an interview with a website in Los Angeles, Richard Sherman once said it was a word constructed in the same way he and his brother used to make up words in their childhood.
But it says there was an earlier form of the word, supercalafajalistickespialadojus, first documented in a song in 1949.
The song's writers were unsuccessful in taking legal action for alleged copyright infringement against the company that published the Disney song.
Whatever the true origins - and the Shermans always maintained they were unaware of the other song - they popularised the word which, nearly 50 years on, does not seem to have lost its magic.