The Collaborative International Dictionary of English v.0.48:

Attainder \At*tain"der\, n. [OF. ataindre, ateindre, to accuse,
   convict. Attainder is often erroneously referred to F.
   teindre tie stain. See Attaint, Attain.]
   1. The act of attainting, or the state of being attainted;
      the extinction of the civil rights and capacities of a
      person, consequent upon sentence of death or outlawry; as,
      an act of attainder. --Abbott.
      [1913 Webster]

   Note: Formerly attainder was the inseparable consequence of a
         judicial or legislative sentence for treason or felony,
         and involved the forfeiture of all the real and
         personal property of the condemned person, and such
         "corruption of blood" that he could neither receive nor
         transmit by inheritance, nor could he sue or testify in
         any court, or claim any legal protection or rights. In
         England attainders are now abolished, and in the United
         States the Constitution provides that no bill of
         attainder shall be passed; and no attainder of treason
         (in consequence of a judicial sentence) shall work
         corruption of blood or forfeiture, except during the
         life of the person attainted.
         [1913 Webster]

   2. A stain or staining; state of being in dishonor or
      condemnation. [Obs.]
      [1913 Webster]

            He lived from all attainder of suspect. --Shak.
      [1913 Webster]

   Bill of attainder, a bill brought into, or passed by, a
      legislative body, condemning a person to death or
      outlawry, and attainder, without judicial sentence.
      [1913 Webster]

WordNet (r) 3.0 (2006):

attainder
    n 1: cancellation of civil rights [syn: attainder, civil
         death]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ATTAINDER, English criminal law. Attinctura, the stain or corruption of
blood which arises from being condemned for any crime.
     2. Attainder by confession, is either by pleading guilty at the bar
before the judges, and not putting one's self on one's trial by a jury; or
before the coroner in sanctuary, when in ancient times, the offender was
obliged to abjure the realm.
     3. Attainder by verdict, is when the prisoner at the bar pleads not
guilty to the indictment, and is pronounced guilty by the verdict of the
jury.
     4. Attainder by process or outlawry, is when the party flies, and is
subsequently outlawed. Co. Lit. 391.
     5. Bill of attainder, is a bill brought into parliament for attainting
persons condemned for high treason. By the constitution of the United
States, art. 1, sect. 9, Sec. 3, it is provided that no bill of attainder or
ex post facto law shall be passed.