Longest english word

Pneumonoultramicroscopicsilicovolcanoconiosis is longest word in English to appear in a major dictionary. Note that there are technical words with 100,000+ letters, that doesn't appear in the dictionary.

It depends on how you define a word. Wikipedia has a good article about it:

http://en.wikipedia.org/wiki/Longest_word_in_English

Personally I think the winner must be Floccinaucinihilipilification, which means, um... er...

Rivid is right with pneumonoultramicroscopicsilicovolcanoconiosis at 45 letters. I found a similar discussion on the english forums: Longest word in the English language which is quite long with 33 pages of answers, so I'm not sure if there is a definite answer to this hehe.