WordNet records no synonym and no antonym for court-martial. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a military court to try members of the armed services who are accused of serious breaches of martial law
a trial that is conducted by a military court
Synonyms, antonyms and the broader and narrower relations for court-martial come from Princeton University’s WordNet. Full sources and licences.