The Collaborative International Dictionary of English v.0.48:

Atone \A*tone"\ ([.a]*t[=o]n"), v. i. [imp. & p. p. Atoned; p.
   pr. & vb. n. Atoning.] [From at one,, i. e., to be, or
   cause to be, at one. See At one.]
   1. To agree; to be in accordance; to accord. [Obs.]
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            He and Aufidius can no more atone
            Than violentest contrariety.          --Shak.
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   2. To stand as an equivalent; to make reparation,
      compensation, or amends, for an offense or a crime.
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            The murderer fell, and blood atoned for blood.
                                                  --Pope.
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            The ministry not atoning for their former conduct by
            any wise or popular measure.          --Junius.
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The Collaborative International Dictionary of English v.0.48:

Atone \A*tone"\, v. t.
   1. To set at one; to reduce to concord; to reconcile, as
      parties at variance; to appease. [Obs.]
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            I would do much
            To atone them, for the love I bear to Cassio.
                                                  --Shak.
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   2. To unite in making. [Obs. & R.]
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            The four elements . . . have atoned
            A noble league.                       --Ford.
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   3. To make satisfaction for; to expiate.
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            Or each atone his guilty love with life. --Pope.
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WordNet (r) 3.0 (2006):

atone
    v 1: make amends for; "expiate one's sins" [syn: expiate,
         aby, abye, atone]
    2: turn away from sin or do penitence [syn: repent, atone]