WordNet records no synonym and no antonym for retrial. It is the only member of its synset, 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 new trial in which issues already litigated and to which the court has already rendered a verdict or decision are reexamined by the same court; occurs when the initial trial is found to have been improper or unfair due to procedural errors
Synonyms, antonyms and the broader and narrower relations for retrial come from Princeton University’s WordNet. Full sources and licences.