What is an antonym for Nation?

There isn't a perfect antonym for "nation" in the sense of a single word. However, depending on the context, you could use words that convey the opposite idea, such as:

Based on size:

* Tribe: A small, localized group of people.

* Clan: A group of families with a common ancestor.

* Community: A group of people living in the same place or sharing a common interest.

Based on organization:

* Chaos: A state of complete disorder and confusion.

* Anarchy: A state of lawlessness and disorder.

* Disunity: A lack of agreement or cooperation.

Based on power:

* Individual: A single person, as opposed to a collective.

* Rebellion: An act of resistance against authority.

* Oppression: The act of subjecting someone to unjust or cruel treatment.

Based on identity:

* Alien: A person from a different country.

* Foreigner: A person who is not a citizen of the country they are in.

* Outsider: A person who is not part of a group.

The best antonym will depend on the specific context and the meaning you want to convey.