Pneumonoultramicroscopicsilicovolcanoconiosis, the longest English word appearing in a major English dictionary, contains 45 letters. You can hear it pronounced at http://en.wiktionary.org/wiki/pneumonoultramicroscopicsilicovolcanoconiosis
The chemical name for titin, which is the largest known protein, is touted at the longest word in English though. It actually contains 189,819 letters when spelled out into its full form. Try pronouncing that. :)
For more info on long English words, see http://en.wikipedia.org/wiki/Longest_word_in_English
Wanna hear the longest Polish word? :D Konstantynopolitańczykowianeczka
I like: floccinaucinihilipilification, which I actually used in an essay :D
It means "The action or habit of estimating something as worthless". It's interesting as it is made up of a number of latin words, that all mean 'of little worth' or 'small'.
A more interesting question might be: what's the longest word you have personally <em>used</em>, just as a regular word that you needed to use--not in a discussion of long words?
In my case, <em>probably</em>: desoxyribonucleic acid.
Hahahaha. Agreed, Paul. :)
The same word is also the longest in portuguese: pneumoultramicroscopicossilicovulcanoconiótico
However we had another big word before: anticonstitucionalissimamente
