-arian refers to a person who supports a particular idea : as in 'vegetarian' -ism refers to a movement or ideology : as in 'socialism'. The meaning of this word is something that you'll find quite boring. It's to do with views about the powers of the church within Great Britain. The most interesting thing about it is the word itself, which is indeed the longest 'real' and non-technical word in the English language.

-Arian roughly means "of or relating to" or used to name a person of a political party. The word "agrarian" means of or related to farming or a member of the Agrarian political party. -ism is used to reference the idea of something, usually more philosophical. "Patriotism" is the idea of being patriotic and loving your country. "Communism" is the idea of living together as one, in a "commune". "Disestablimentarian" is someone in a political party that is against an "establishment", an organization that holds a lot of power in a country, like a national church. "Anti-" means against so "antidisestablishmentarianism" means the idea of being against the political ideas of an establishmentarian.