This post turned out to be surprisingly popular, so I rewrote it to include not only the longest word but also a few other linguistic anomalies - a hill name 85 letters long for example. Happy reading...
The longest word turned out to be a scientific one, a full name of a protein - Titin, also known as connectin. It is 189,819 letters long. Professional dictionary writers regard generic names of chemical compounds as verbal formula rather than as English words, so it is a bit disputable if this can be viewed as a true word. it is too long to post here, so I am posting a shorter one instead - this one is only 1185 letters long:
The longest word coined by a major author is a name of a fictional dish (183 letters):
The longest officially recognized place name is a name of a hill in New Zealand (85 letters):
The name is often shortened to Taumata by the locals for ease of conversation. It translates roughly as "The summit where Tamatea, the man with the big knees, the climber of mountains, the land-swallower who traveled about, played his nose flute to his loved one".
The is some disute about this word status - as of now wikipedia claims that the longest non coined and not technical word is (28 letters):
Source - wikipedia.