Haha, that's alright, I think there are about six or seven versions of this word on the site, but only one (the one I linked to) is "correct." Not that correctness really matters here, since it's admittedly a joke word, but whatever. ;-)
pneumonoultramicroscopicsilicovolcanoconiosis n. (also pneumonoultramicroscopicsilicovolcanokoniosis) (cf. PNEUMONOCONIOSIS n.) a word invented (prob. by Everett M. Smith (born 1894), president of the National Puzzlers' League in 1935) in imitation of polysyllabic medical terms, alleged to mean ‘a lung disease caused by the inhalation of very fine sand and ash dust’ but occurring only as an instance of a very long word.