E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A cake of wax or dough stamped with the figure of a lamb supporting the banner of the Cross, and distributed by the Pope on the Sunday after Easter as an amulet. Our Lord is called Agnus Dei (the Lamb of God). There is also a prayer so called, because it begins with the words, Agnus Dei, qui tollis peccata mundi (O Lamb of God, that takest away the sins of the world).