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.
To expiate his treason, hath naught left. --Milton.
The Treasurer obliged himself to expiate the injury.
2. To purify with sacred rites. [Obs.]
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.