Supercalifragilisticexpialidocious
(pronounced /ˌsuːpərˌkælɪˌfrædʒəlˌɪstɪkˌɛkspiːˌælɪˈdoʊʃəs/) is an English word in the song with the same title in the musical film Mary Poppins. The song was written by the Sherman Brothers, and sung by Julie Andrews and Dick van Dyke. It also appears in the stage show version of Mary Poppins.
Since Mary Poppins was a period piece set in 1910, period sounding songs were wanted. Supercalifragilisticexpialidocious sounds like contemporary music hall songs "Boiled Beef and Carrots" and "Any Old Iron".
Origin
According to Richard M. Sherman, co-writer of the song with his brother, Robert, the word was created by them in two weeks, mostly out of double-talk.
The roots of the word have been defined[3] as follows: super- "above", cali- "beauty", fragilistic- "delicate", expiali- "to atone", and docious- "educable", with the sum of these parts signifying roughly "Atoning for educability through delicate beauty." Although the word contains recognizable English morphemes, it does not follow the rules of English morphology as a whole. The morpheme -istic is a suffix in English, whereas the morpheme ex- is typically a prefix; so following normal English morphological rules, it would represent two words: supercalifragilistic and expialidocious. The pronunciation also leans towards it being two words since, the letter c doesn't normally sound like a k when followed by an e, an i or a y.
According to the 1964 Walt Disney film, it is defined as "what you say when you don't know what to say".
In the 1942 movie The Undying Monster (directed by John Brahm), the character Rob Curtis (played by James Ellison) says of character Christy, "She has an overactive supercalifragilis." He goes on to define the word as "female intuition." This passage does not appear in the 1936 novel by Jessie Douglas Kerruish. The screenplay was written by Lillie Hayward and Michael Jacoby.
https://en.wikipedia.org/wiki/Supercalifragilisticexpialidocious