Court martial refers to the military judicial system where military personnel accused of violating laws are tried in front of a special court. If you want to avoid repeating the same phrase often, you could use synonyms such as "military tribunal," "military court," "admiralty court," "tribunal," and "court of inquiry." These synonyms convey the same meaning and can be used inter-changeably depending on the context. Using synonyms for court martial can add variety and depth to your writing. Just make sure to choose words that accurately reflect the specific aspect of the military court system that you want to convey.