Noun
a legislative act finding a person guilty of treason or felony without a trial
Source: WordNetbills of attainder are prohibited by the Constitution of the United States Source: Internet
A bill of attainder is a law by which a person is immediately convicted without trial. Source: Internet
Cromwell was arraigned under a bill of attainder and executed for treason and heresy on Tower Hill on 28 July 1540. Source: Internet