incommunicado

The word incommunicado describes a state in which a person is cut off from communication with the outside world. It comes from the Spanish word incomunicado and was first used especially for prisoners who were not allowed to speak with other people or send and receive messages. In that setting, the separation was usually imposed by guards or authorities.

That serious meaning is still the main one today. You might read that a political prisoner was held incommunicado, meaning no visits, no calls, and no contact with family or lawyers. The word can also be used more broadly for someone who shuts themselves away and does not answer anyone for a while, but it still suggests a complete or near-complete break in contact.

What matters is not just that the person is hard to reach, but that communication has been fully blocked or stopped. Someone whose phone battery dies is usually just temporarily unreachable. By contrast, someone who is being kept from all outside contact, or someone who has completely cut themselves off, could be described as incommunicado.

So if a person disappears from contact and no messages can get in or out, they may be incommunicado. The word has a formal, serious tone and is most at home in legal, political, and news-related contexts.