Antidisestablishmentarianism is a quite a difficult word to read, spell or pronounce. It is a real word, with a real historical use, and is often considered the longest true word in use in the English language, containing 28 letters. There is a longer word, Floccinaucinihilipilification, which refers to the process of describing or estimating something as worthless, but the word is not commonly used, and moreover is somewhat of an invented word by a few students at Eton College.

Many may wonder why antidisestablishmentarianism is not simply establishmentarianism, since anti and dis create double negatives. The reason you get this huge double negative word is primarily the result of a group of people in the UK who were called disestablishmentarians. Disestablishmentarians in the late 19th and early 20th centuries wanted to see England and the British Isles remove the status of the Church of England or Anglican Church, as the state church. Several measures beginning in the 1800s were placed before parliament to remove the Church of England (also called the Church of Ireland, Scotland and Wales), from being the one religion and church recognized by the state.

Those who opposed disestablishmentarians, and there were many, particularly in Ireland and Wales, were thus supporters of antidisestablishmentarianism. In other words, they wanted the English state to only recognize the Anglican Church as the state church. Eventually in the 1870s, the antidisestablishmentarianism movement failed in Ireland, and the Anglican Church was no longer the state church. Antidisestablishmentarians held out much longer in Wales, and the church there was not disestablished until the 1920s.

Since the term is so specific to a period in history, it's usually only used in reference to Anglican or English history, or to really impress your friends! If you can spell it, you’re certainly proving your prowess as a speller, but you won’t find many ways to casually insert the word into conversation.

Antidisestablishmentarianism is not actually the longest word in the English language. There are many scientific terms that are longer and get greater use in the scientific community. It is a catchy word though, that has never quite been forgotten because of its impressive length.