There are a few different synonyms for the term "courtmartial", which generally refers to a military legal proceeding used to try alleged offenses by service members. One common synonym that is often used is "military tribunal", which carries a similar connotation of a formal legal hearing. Another related term is "military court", which can also refer to the same type of proceeding or to the court system as a whole. Other possible synonyms for courtmartial might include "military trial", "service trial", or "disciplinary hearing", all of which could be used in different contexts depending on the specific case or legal procedure in question.