to eradicate the guilt incurred by (a sin, etc)
to pay the penalty for (a crime, etc)
to make amends for (something)
expiable adj
expiation /-ʹaysh(ə)n/ noun
expiator noun
expiatory /ekspiʹayt(ə)ri, ʹekspi·ət(ə)ri/ adj
[Latin expiatus, past part. of expiare to atone for, from ex-1 + piare to atone for, appease]