Excommunication is the name of the church punishment, or the state of already being outside. It is the noun that belongs to the verb excommunicate — not “to punish,” but the act and the condition. A bishop may threaten excommunication; a person may live under it. In history it could sound like a weapon: if a pope used it against a king, people who believed they needed the church for their souls were genuinely afraid. The practice still exists in some church law, but you will hear the word more in news and textbooks than at the dinner table. Some writers stretch it to mean being cut off from any group. Though actually that use is informal and a bit dramatic; the home meaning is church law.