From Longman Dictionary of Contemporary Englishkangaroo courtˌkangaroo ˈcourt noun [countable] SCTPUNISHan unofficial court that punishes people unfairly
Examples from the Corpus
kangaroo court• It's grossly unfair for television to single out one player from one game and conduct a kangaroo court there and then.• It was like a kangaroo court, he thought.• He leads the reader into assuming that the tribunal is anything other than a kangaroo court.• He was fined recently in kangaroo court and the pitchers offered to pay it.• The kangaroo court decided the punishment must fit the crime and ruled that he stay in his cell during the jailhouse comedy. 