Agnus-castus
.A shrub of the Vitex tribe, called agnos (chaste) by the Greeks, because the Athenian ladies, at the feast of Cerēs, used to strew their couches with vitex leaves, as a palladium of chastity. The monks, mistaking agnos (chaste) for agnus (a lamb), but knowing the use made of the plant, added castus to explain its character, making it chaste-lamb. (For another similar blunder, see I.H.S.)