The term "g.i." has various synonyms depending on the context it is being used. In medicine, GI is a well-known abbreviation for the gastrointestinal system, which refers to the digestive system. In military terms, G.I is used to refer to a government-issued soldier or military personnel, while in slang, G.I refers to a person from the United States. Other synonyms for G.I include army man, serviceman, veteran, trooper, soldier, GI Joe, and grunt, among others. It's crucial to understand the context in which the term is being used to determine the appropriate synonym to apply.