1The plant Vitex agnus-castus or various of its parts (flowers, leaves, seeds, etc.) used as a herbal medicine, originally to reduce sexual potency or desire, and later mainly to treat menstrual and menopausal symptoms.
2An aromatic shrub, Vitex agnus-castus (family Verbenaceae), native to the Mediterranean region and central Asia, which has digitate leaves, tall spikes of lilac-coloured flowers, and small round reddish-black berries; also called chaste tree. In early use also: †the plant tutsan, Hypericum androsaemum (family Hypericaceae), with reddish leaves and yellow flowers (obsolete).
Late Middle English; earliest use found in John Trevisa (c1342–?1402), translator. From post-classical Latin agnus castus from agnus + classical Latin castus chaste.