Source : Webster's Revised Unabridged Dictionary (1913)

Atonement \A*tone"ment\, n.

   {Day of Atonement} (Jewish Antiq.), the only fast day of the
      Mosaic ritual, celebrated on the tenth day of the seventh
      month (Tisri), according to the rites described in
      Leviticus xvi. Atrium \A"tri*um\, n. (Anat.)
   A cavity, entrance, or passage; as, the atrium, or atrial
   cavity, in the body wall of the amphioxus; an atrium of the
   infundibula of the lungs, etc.

Atonement \A*tone"ment\, n.
   1. (Literally, a setting at one.) Reconciliation; restoration
      of friendly relations; agreement; concord. [Archaic]

            By whom we have now received the atonement. --Rom.
                                                  v. 11.

            He desires to make atonement Betwixt the Duke of
            Gloucester and your brothers.         --Shak.

   2. Satisfaction or reparation made by giving an equivalent
      for an injury, or by doing of suffering that which will be
      received in satisfaction for an offense or injury;
      expiation; amends; -- with for. Specifically, in theology:
      The expiation of sin made by the obedience, personal
      suffering, and death of Christ.

            When a man has been guilty of any vice, the best
            atonement be can make for it is, to warn others.
                                                  --Spectator.

            The Phocians behaved with, so much gallantry, that
            they were thought to have made a sufficient
            atonement for their former offense.   --Potter.

Source : WordNet®

atonement
     n 1: compensation for a wrong; "we were unable to get
          satisfaction from the local store" [syn: {expiation}, {satisfaction}]
     2: the act of atoning for sin or wrongdoing (especially
        appeasing a deity) [syn: {expiation}, {propitiation}]