Woad
Woad, an herb of the mustard family. The ancient Britons ground woad to get blue dye, which they used to stain their bodies before battle. They hoped their appearance would terrify the enemy. Woad is still cultivated in some parts of Europe, but it has been replaced as a dye by indigo and by synthetic dyes. The plant grows erect, 18 to 36 inches (45 to 90 cm) high.
Woad is Isis tinctoria of the family Cruciferae.