Real Dictionary

kangaroo court
countable noun: If you refer to a court or a meeting as a kangaroo court, you disapprove of it because it is unofficial or unfair, and is intended to find someone guilty.

kangaroo court in American English
an unauthorized, irregular court, usually disregarding normal legal procedure, as one in a frontier region
noun: a self-appointed or mob-operated tribunal that disregards or parodies existing principles of law or human rights, esp. one in a frontier area or among criminals in prison

kangaroo court in British English
noun: an irregular court, esp one set up by prisoners in a jail or by strikers to judge strikebreakers