What is Attaint?

Legal Definition
English law. 1. Atinctus, attainted, stained, or blackened. 2. A writ which lies to inquire whether a jury of twelve men gave a false verdict. Bract. lib. 4, tr. 1, c. 134; Fleta, lib. 5, c. 22, 8.

2. It was a trial by jury of twenty-four men empanelled to try the goodness, of a former verdict. 3 Bl. Com. 351; 3 Gilb. Ev. by Lofft, 1146. See Assize.
-- Bouviers Law Dictionary
Legal Definition
In old English practice. A writ which lay to inquire whether a jury of twelve men had given a false verdict, in order that the judgment might be reversed. 3 Bl. Comm. 402; Bract, fol. 28Sb-292. Tins inquiry was made by a grand assise or jury of twenty-four persons, and, If they found the verdict a false one, the judgment wat that the jurors shonid become infamous, should forfeit their goods and the profits of their lands, should themselves be imprisoned, and their wives and children thrust out of doors, should have their houses razed, their trees extirpated, and their meadows plowed up, and that the plaintiff should be restored to all that he lost by reason of the unjust verdict 3 Bl. Comm. 404; Co. Litt 294b. A person was said to be attaint when he was under attainder, (q. v.) Co. Litt. 390b,
-- Black's Law Dictionary
Legal Definition
A writ employed to reverse a jury’s verdict.
-- Ballentine's Law Dictionary