Longest in Dictionaries
Pneumonoultramicroscopicsilicovolcanoconiosis (45 letters): A lung disease from volcanic dust.
Other Notable Long Words
Supercalifragilisticexpialidocious (34 letters): From Mary Poppins, meaning "extraordinarily good".
Hippopotomonstrosesquippedaliophobia (36 letters): An ironic name for the fear of long words.
Floccinaucinihilipilification (29 letters): Estimating something as worthless; the longest non-technical coined word in some dictionaries.
Antidisestablishmentarianism (28 letters): Opposition to disestablishing the Church of England; one of the longest non-coined, non-technical words.
Technical & Fictional Words
Titin's Chemical Name: The full chemical name for the protein Titin, containing 189,819 letters, is technically the longest "word," but it's a formula, not a word in common use.
Lopadotemachoselachogaleokranioleipsanodrimhypotrimmatosilphioparaomelitokatakechymenokichlepikossyphophattoperisteralektryonoptekephalliokigklopeleiolagoiosiraiobaphetraganopterygon: A 183-letter fictional dish from Aristophanes' play Assemblywomen, making it the longest word coined by a major author.
There's a word that takes 3hrs to say. It's the chemical name of a protein called Titin or Connectin. It's disputed on whether or not it's actually a word.
