The Collaborative International Dictionary of English v.0.48:

Attaint \At*taint"\, v. t. [imp. & p. p. Attainted; p. pr. &
   vb. n. Attainting.] [OE. atteynten to convict, fr. atteynt,
   OF. ateint, p. p. of ateindre, ataindre. The meanings 3, 4,
   5, and 6 were influenced by a supposed connection with taint.
   See Attain, Attainder.]
   1. To attain; to get act; to hit. [Obs.]
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   2. (Old Law) To find guilty; to convict; -- said esp. of a
      jury on trial for giving a false verdict. [Obs.]
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            Upon sufficient proof attainted of some open act by
            men of his own condition.             --Blackstone.
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   3. (Law) To subject (a person) to the legal condition
      formerly resulting from a sentence of death or outlawry,
      pronounced in respect of treason or felony; to affect by
      attainder.
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            No person shall be attainted of high treason where
            corruption of blood is incurred, but by the oath of
            two witnesses.                        --Stat. 7 & 8
                                                  Wm. III.
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   4. To accuse; to charge with a crime or a dishonorable act.
      [Archaic]
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   5. To affect or infect, as with physical or mental disease or
      with moral contagion; to taint or corrupt.
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            My tender youth was never yet attaint
            With any passion of inflaming love.   --Shak.
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   6. To stain; to obscure; to sully; to disgrace; to cloud with
      infamy.
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            For so exceeding shone his glistring ray,
            That Ph?bus' golden face it did attaint. --Spenser.
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            Lest she with blame her honor should attaint.
                                                  --Spenser.
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The Collaborative International Dictionary of English v.0.48:

Attaint \At*taint"\, p. p.
   Attainted; corrupted. [Obs.] --Shak.
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The Collaborative International Dictionary of English v.0.48:

Attaint \At*taint"\, n. [OF. attainte. See Attaint, v.]
   1. A touch or hit. --Sir W. Scott.
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   2. (Far.) A blow or wound on the leg of a horse, made by
      overreaching. --White.
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   3. (Law) A writ which lies after judgment, to inquire whether
      a jury has given a false verdict in any court of record;
      also, the convicting of the jury so tried. --Bouvier.
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   4. A stain or taint; disgrace. See Taint. --Shak.
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   5. An infecting influence. [R.] --Shak.
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WordNet (r) 3.0 (2006):

attaint
    v 1: bring shame or dishonor upon; "he dishonored his family by
         committing a serious crime" [syn: dishonor, disgrace,
         dishonour, attaint, shame] [ant: honor, honour,
         reward]
    2: condemn by attainder; "the man was attainted"

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

ATTAINT, 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, Sec. 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.