Antidisestablishmentarianism is a political position. It means "to keep an established church". An official state church is called the "established" church, so a disestablishmentarian is a person who wants to stop the state church. These people say a state church hurts the freedom of religion. These people say the state should be secular, meaning religion and the country are separate. This idea is called disestablishmentarianism. So antidisestablishmentarianism wants to keep the state church.