Is supercalifragilisticexpialidocious the longest word in world?

No, "supercalifragilisticexpialidocious" is not the longest word in the world. While it's certainly a long word, it's not even the longest word in the English language!

There are many longer words, including:

* Pneumonoultramicroscopicsilicovolcanoconiosis: This 45-letter word describes a lung disease caused by inhaling very fine silica dust.

* Floccinaucinihilipilification: This 29-letter word means "the act of estimating something as worthless."

* Antidisestablishmentarianism: This 28-letter word refers to opposition to the separation of church and state.

And if you're looking for the absolute longest word in any language, that title goes to "pneumonoultramicroscopicsilicovolcanoconiosis" from the English language, although some languages have even longer words when you account for compound words or technical terms.