The Collaborative International Dictionary of English v.0.48:

Assoil \As*soil"\, v. t. [OF. assoiler, absoiler, assoldre, F.
   absoudre, L. absolvere. See Absolve.]
   1. To set free; to release. [Archaic]
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            Till from her hands the spright assoiled is.
                                                  --Spenser.
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   2. To solve; to clear up. [Obs.]
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            Any child might soon be able to assoil this riddle.
                                                  --Bp. Jewel.
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   3. To set free from guilt; to absolve. [Archaic]
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            Acquitted and assoiled from the guilt. --Dr. H.
                                                  More.
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            Many persons think themselves fairly assoiled,
            because they are . . . not of scandalous lives.
                                                  --Jer. Taylor.
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   4. To expiate; to atone for. [Archaic] --Spenser.
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            Let each act assoil a fault.          --E. Arnold.
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   5. To remove; to put off. [Obs.]
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            She soundly slept, and careful thoughts did quite
            assoil.                               --Spenser.
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The Collaborative International Dictionary of English v.0.48:

Assoil \As*soil"\, v. t. [Pref. ad- + soil.]
   To soil; to stain. [Obs. or Poet.] --Beau. & Fl.
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         Ne'er assoil my cobwebbed shield.        --Wordsworth.
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WordNet (r) 3.0 (2006):

assoil
    v 1: pronounce not guilty of criminal charges; "The suspect was
         cleared of the murder charges" [syn: acquit, assoil,
         clear, discharge, exonerate, exculpate] [ant:
         convict]