The phrase "in stir" is often used to describe someone who is in prison or jail. However, there are a number of synonyms that can be used to convey the same meaning. For example, one might say that someone is "behind bars" or "doing time" to mean that they are in prison. Similarly, "in custody" or "locked up" could also be used to describe someone who is in jail. Other phrases, like "under arrest" or "detained," could also be used to convey the idea that someone is being held by law enforcement. Regardless of the phrasing used, these synonyms all speak to the same basic idea: that someone is not free to move about due to a criminal charge or conviction.