Longman Dictionary of Contemporary English
Wiktionary
n. A trial held for appearance's sake, but for which the verdict is predetermined; ''especially'' when the verdict is "guilty", and the purpose of the trial is to make an example of the accused. (1937)
WordNet
n. a trial held for show; the guilt of the accused person has been decided in advance
Wikipedia
A show trial is a public trial in which the judicial authorities have already determined the guilt of the defendant. The actual trial has as its only goal to present the accusation and the verdict to the public as an impressive example and as a warning to other would-be dissidents or transgressors. Show trials tend to be retributive rather than correctional justice and also conducted for propagandistic purposes. The term was first recorded in the 1930s.
Usage examples of "show trial".
Diana had been remanded in custody for a month before they saw reason, her reason, and decided against the embarrassment a show trial would create.
Back during the halcyon days when SCOFLA thought it was immune from review, the court's hearings resembled nothing so much as a Soviet show trial.
The best you could hope for would be a show trial and a swift execution.
They'd picked him for the show trial, not for infiltrating the opposition.
They resented the independence of the military and staged show trial after show trial to cow resistance.
Artukovic's presence on his native soil had stirred old memories, and the Communist authorities had responded only with a poorly managed, Stalinist-style show trial that served to inflame passions on the related Stepinac issue.
There are still powers that be who want Valentine brought back alive for a show trial.