The definition of antidisestablishmentarianism according to the Cambridge Dictionary is ‘opposition to the belief that there should not be an official relationship between a country’s government and its national Church‘.
The word is a noun in this context, specifically a singular noun i.e. a noun with no plural of the word.
The word antidisestablishmentarianism is used in politics and has a powerful meaning. The word was also used in the opening gambit of an ICE-T track!