The Collaborative International Dictionary of English v.0.48:
Expiatory \Ex"pi*a*to*ry\, a. [L. expiatorius: cf. F. expiatoire.] Having power, or intended, to make expiation; atoning; as, an expiatory sacrifice. [1913 Webster]WordNet (r) 3.0 (2006):
expiatory adj 1: having power to atone for or offered by way of expiation or propitiation; "expiatory (or propitiatory) sacrifice" [syn: expiatory, expiative, propitiatory]