a legislative enactment by which a person is pronounced guilty, without trial, of an alleged crime, orig. a capital crime, esp. treason: prohibited in the U.S. by the Constitution
See bill of attainder in American Heritage Dictionary 4
nounpl.bills of attainder
A legislative act pronouncing a person guilty of a crime, usually treason, without trial and subjecting that person to capital punishment and attainder. Such acts are prohibited by the U.S. Constitution.