You didn't have to bump this, but I know the longest word in history :D It's the chemical name for Titin. I will not post it since I'd get a placeholder for the longest forum pagestretch in history then get permabanned.
With one houndred eighty eight thousand eight houndred nineteen letters (because writing 188.819 in letters makes it seem that much longer) it holds the record of the longest word on earth.
Edit: Darn, pilojo and mastermind beat me to it. BUT I CREATED A PASTEBIN WITH IT >:D http://pastebin.com/hW5jn2v0