Called Abraham's balm. Agnus Castus, and the chaste-tree. In the language of flowers it means
“insensibility to love.” Dioscorides, Pliny, and Galen mention the plant, and say that the Athenian ladies, at the feast of Ceres, used to strew their couches with vitex leaves as a palladium of chastity. In France a beverage is made of the leaves by distillation, and is (or was at one time) given to novitiates to wean their hearts from earthly affections. Vitex, from vico, to bind with twigs; so called from the flexible nature of the twigs.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894