What is the longest word in the dictionary, and what is the definition?

Answer 1

The longest word in any major English language dictionary is pneumono­ultra­micro­scopic­silico­volcano­coniosis, a 45-letter word supposed to refer to a lung disease contracted from the inhalation of volcanic ash, but research has discovered that this word was originally intended as a hoax. It has since been used in a close approximation of its originally intended meaning, lending at least some degree of validity to its claim.[1]
The Oxford English Dictionary contains pseudopseudohypoparathyroidism (30 letters).
The longest non-technical word is flocci­nauci­nihili­pili­fication at 29 letters. Consisting of a series of Latin words meaning "nothing" and defined as "the act of estimating something as worthless," its usage has been recorded as far back as 1741.[2][3][4] In recent times its usage has been recorded in the proceedings of the United States Senate by Senator Robert Byrd [5], and at the White House by Bill Clinton's press secretary Mike McCurry, albeit sarcastically.[6]
Anti­dis­establishment­arianism (a nineteenth century movement in England opposed to the separation of church and state) at 28 letters is still in colloquial currency for being one of the longest words in the English language.
The longest word which appears in William Shakespeare's works is the 27-letter honorific­abilitud­initatibus, appearing in Love's Labour's Lost. This is arguably an English word (rather than Latin), but only because it was Shakespeare who used it.
The humuhumu-nukunuku-a-pua‘a, or reef triggerfish, is Hawaii's official state fish.[7] At 22 letters (including the okina) it is one of the best known very long one-word names for an animal. It is occasionally quipped that the name is longer than the fish.
Although only fourteen letters long, sesquipedalian deserves a mention. It is derived from a nonce word used by the Roman author Horace, in his work Ars Poetica (The Art of Poetry). The quote is as follows: "Proicit ampullas et sesquipedalia verba," which means, "He throws aside his paint pots and his words that are a foot and a half long." The Oxford English Dictionary lists sesquipedalianism ("the practice of using words one and a half feet long"),

In his play Ecclesiazousae ("The Assemblywomen"), the ancient Greek comedic playwright Aristophanes created: Lopadotemachoselachogaleokranioleipsanodrimhypotrimmatosilphio-paraomelitokatakechymenokichlepikossyphophattoperisteralektryonop-tekephalliokigklopeleiolagoiosiraiobaphetraganopterygon, a word of 183 letters that describes a dish by stringing together its ingredients.
Henry Carey's farce Chrononhotonthologos (1743) holds the opening line: "Aldiborontiphoscophornio! Where left you Chrononhotonthologos?"
James Joyce made up nine 100 and one 101-letter words in his novel Finnegans Wake, the most famous of which is Bababadal­gharagh­takammin­arronn­konn­bronn­tonn­erronn­tuonn­thunn­trovarrhoun­awnskawn­toohoo­hoordenen­thurnuk. Appearing on the first page, it allegedly represents the symbolic thunderclap associated with the fall of Adam and Eve. As it appears nowhere else except in this passage, it is generally not accepted as a real word. Sylvia Plath made mention of it in her semi-autobiographical novel The Bell Jar, when the protagonist was reading Finnegans Wake.
"Supercalifragilisticexpialidocious", the 34-letter title of a song from the movie Mary Poppins, does appear in several dictionaries, but only as a proper noun defined in reference to the song title. The attributed meaning is "a word that you say when you don't know what to say." The idea and invention of the word is credited to songwriters Robert and Richard Sherman.

Answer 2

Antidisestablishmententarianism. I have no idea what it means. Just had to learn to spell it in 4th grade!

The 2 people who answered with the lung thing... that word is in a medical dictionary... not a normal one!

Answer 3

Pneumonoultramicroscopic silicovolcano coniosis (also spelled -koniosis) is an alleged lung disease caused by the inhalation of very fine silica dust found in volcanoes

I had to put spaces in it, because Yahoo cut it off!