A resident alien is a non-citizen who resides legally in a country other than their own. However, there are several synonyms for this term that can be used interchangeably. One of the most common synonyms is "non-immigrant alien." This term is often used in the United States to describe non-citizens who are living in the country for short periods of time, such as students or temporary workers. Other synonyms include "non-citizen resident," "foreign resident," and "non-native resident." Each of these terms conveys the same basic idea - a person who is legally living in a country where they are not a citizen.