The longest word in literature is the fictional dish described in Aristophanes’ comedy Assemblywomen, written in around 391 BC.
λοπαδοτεμαχοσελαχογαλεοκρανιολειψανοδριμυποτριμματοσιλφιοκαραβομελιτοκατακεχυμενοκιχλεπικοσσυφοφαττοπεριστεραλεκτρυονοπτοκεφαλλιοκιγκλοπελειολαγῳοσιραιοβαφητραγανοπτερύγων
which is the name of a dish compounded of all kinds of dainties, fish, flesh, fowl, and sauces.
which, in the Roman alphabet is written as:
Lopadotemachoselachogaleokranioleipsanodrimhypotrimmatosilphioparaomelitokatakechymenokichlepikossyphophattoperisteralektryonoptekephalliokigklopeleiolagoiosiraiobaphetraganopterygo
with a rough English translation of:
oysters-saltfish-skate-sharks’-heads-left-over-vinegar-dressing-laserpitium-leek-with-honey-sauce-thrush-blackbird-pigeon-dove-roast-cock’s-brains-wagtail-cushat-hare-stewed-in-new-wine-gristle-of-veal-pullet’s-wings
Leo Strauss (1966)
The longest non-technical word in English is:
floccinaucinihilipilification
meaning: the act of estimating something as worthless.