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Old English wad, from Proto-Germanic *waido- (cf. Danish vaid, Old Frisian wed, Middle Dutch wede, Dutch wede, Old High German weit, German Waid "woad"), probably cognate with Latin vitrium "glass" (see vitreous). Old type of blue dye processed from plant leaves, since superseded by indigo. French guède, Italian guado are Germanic loan-words.
(Isatis tinctoria), biennial or perennial herb, in a genus of about 80 species in the mustard family (Brassicaceae), formerly grown as a source of the blue dye indigo and now sometimes cultivated for its small, four-petalled yellow flowers. It is a summer-flowering native of Eurasia, now naturalized in southeastern North America. Woad reaches 90 cm (3 feet) and produces clusters of dangling, winged, oval, single-seeded fruits. The hairy stem leaves have arrow-shaped bases; the long basal leaves are downy and lance shaped. The ground and dried leaves, when wetted and fermented, produce indigotin.