At common law, Attainder means the act of extinguishing a person’s civil rights when that person is sentenced to death or declared an outlaw for committing felony or treason. In History, it refers to a grand jury proceeding to try if a jury has given a false verdict. It also refers to the conviction of a jury so tried.
Attainder is derived from the Latin term “attinctus” which means stained or polluted. It includes all the disabilities that flow from a capital sentence. On the attainder, the defendant is disqualified from being a witness in court; s/he cannot bring any action or perform any legal functions. In short the person is regarded as dead in law.