Floccinaucinihilipilification is one of a number of very long words that occur very rarely in genuine use. Based on Latin [Term?]: flocci (“wisp”) +‎ nauci (“trifle”) +‎ nihil (“nothing”) +‎ pili (“hair”) +‎ -ficationA jocular coinage, apparently by pupils at Eton College, combining a number of roughly synonymous Latin stems. Often cited as the longest non-technical word in the English language, being one letter longer than the commonly cited antidisestablishmentarianism.

The word was inspired by a line in the Eton Latin Grammar that gave a rule for certain verbs that take an object in the genitive case: “flocci, nauci, nihilī, pilī, assis, huius, teruncii, hīs verbīs, aestimō, pendō, faciō, pecūliāriter adduntur”. This translates loosely to: “The verbs aestimo, pendo and facio when used in the sense of “to value” or “to care” irregularly take the following objects in the genitive case: flocci, nauci, nihilī, pilī, assis (“penny”), huius (“this”) and teruncii (“farthing”)”.

Source: https://en.wiktionary.org/wiki/floccinaucinihilipilification