Long Words
SUBDERMATOGLYPHIC
At 17 characters, this is the longest accepted isogram, a word in which every letter is used only once, and refers to the underlying dermal matrix that determines the pattern formed by the whorls, arches, and ridges of our fingerprints.
PNEUMONOULTRAMICROSCOPICSILICOVOLCANOCONIOSIS
At 45 letters, this is the longest word you'll find in a major dictionary. An inflated version of silicosis, this is the full scientific name for a disease that causes inflammation in the lungs owing to the inhalation of very fine silica dust. Despite its inclusion in the dictionary, it's generally considered superfluous, having been coined simply to claim the title of the longest English word.
FLOCCINAUCINIHILIPILIFICATION
By virtue of having one more letter than antidisestablishmentarianism, this is the longest non-technical English word. A mash up of five Latin roots, it refers to the act of describing something as having little or no value. While it made the cut in the Oxford English Dictionary, Merriam-Webster volumes refuse to recognize it, chalking up its existence to little more than linguistic ephemera.
METHIONYLTHREONYLTHREONYGLUTAMINYLARGINYL...ISOLEUCINE
Note the ellipses. All told, the full chemical name for the human protein titin is 189,819 letters, and takes about three-and-a-half hours to pronounce. The problem with including chemical names is that there's essentially no limit to how long they can be. For example, naming a single strand of DNA, with its millions and millions of repeating base pairs, could eventually tab out at well over a billion letters.
PARASTRATIOSPHECOMYIA STRATIOSPHECOMYIOIDES
The longest accepted binomial construction, at 42 letters, is a species of soldier fly native to Thailand. With a lifespan of five to eight days, it's unlikely one has ever survived long enough to hear it pronounced correctly.
LOPADOTEMACHOSELACHOGALEOKRANIOLEIPSAN...PTERYGON
The longest word ever to appear in literature comes from Aristophanes' play, Assemblywomen, published in 391 BC. The Greek word tallies 171 letters, but translates to 183 in English. This mouthful refers to a fictional fricassee comprised of rotted dogfish head, wrasse, wood pigeon, and the roasted head of a dabchick, among other culinary morsels
PSEUDOPSEUDOHYPOPARATHYROIDISM
This 30-letter thyroid disorder is the longest non-coined word to appear in a major dictionary