The identity of the longest word in English depends on the definition of a word and of length.
Parastratiosphecomyia stratiosphecomyioides
The sign at Taumatawhakatangihangakoauauotamateaturipukakapikimaungahoronukupokaiwhenuakitanatahu
The station sign at Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch in North Wales
Supercalifragilisticexpialidocious
"Supercalifragilisticexpialidocious" is a song and single from the 1964 Disney musical film Mary Poppins. It was written by the Sherman Brothers, and sung by Julie Andrews and Dick Van Dyke. It also appears in the 2004 stage show version.
Because Mary Poppins was a period piece set in 1910, songs that sounded similar to songs of the period were wanted. The movie version finished at #36 in AFI's 100 Years...100 Songs survey of top tunes in American cinema.
1964 US single