While that word is definitely long, the title of "longest word" is often awarded to pneumonoultramicroscopicsilicovolcanoconiosis, a lung disease caused by inhaling very fine silica dust.
There are actually a few contenders for the longest word, depending on how you define "word." For example, some argue that "floccinaucinihilipilification" (the act of estimating something as worthless) is also a valid candidate.
Ultimately, the "longest word" is a bit of a subjective title, but these two words are definitely up there in terms of length and obscurity!