The Collaborative International Dictionary of English v.0.48:

Expiate \Ex"pi*ate\, v. t. [imp. & p. p. Expiated; p. pr. &
   vb. n. Expiating.] [L. expiatus, p. p. of expiare to
   expiate; ex out + piare to seek to appease, to purify with
   sacred rites, fr. pius pious. See Pious.]
   1. To extinguish the guilt of by sufferance of penalty or
      some equivalent; to make complete satisfaction for; to
      atone for; to make amends for; to make expiation for; as,
      to expiate a crime, a guilt, or sin.
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            To expiate his treason, hath naught left. --Milton.
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            The Treasurer obliged himself to expiate the injury.
                                                  --Clarendon.
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   2. To purify with sacred rites. [Obs.]
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            Neither let there be found among you any one that
            shall expiate his son or daughter, making them to
            pass through the fire.                --Deut. xviii.
                                                  10 (Douay
                                                  version)
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