Antidisestablishmentarianism is a political philosophy that is opposed to the separation of church and state. The term originated in the context of the nineteenth century Church of England, where "antidisestablishmentarians" were opposed to proposals to remove its status as the state church of England. Antidisestablishmentarianism succeeded in England, but failed in Ireland and Wales, with the Church of Ireland being disestablished in 1871 and the Church in Wales in 1920. The term has largely fallen into disuse, although the issue itself is still current (see Act of Settlement).

Antidisestablishmentarianism is often quoted as one of the longest English words that has an actual meaning (as opposed to words that were made up for the purpose of being long), although there are longer words that fall in the same category: Pseudoantidisestablishmentarianism, meaning 'false opposition to the separation of the state and the church.' Antidisestablishmentarianism could also be indefinitely prefixed or suffixed with any of various formative prefixes or grammatical suffixes: contra-, neo-, -ly, etc., one after another, yielding perhaps a monstrosity such as contra-neo-pseudo-anti-dis-establish-ment-ari-an-ist-ic-ally.

See also

• Disestablishmentarianism
• Religion in the United Kingdom