woad /ˈwod/
 大青;菘藍;藍色染料
 Woad n.  [Written also wad, and wade.]
 1. Bot. An herbaceous cruciferous plant (Isatis tinctoria) of the family Cruciferae (syn. Brassicaceae). It was formerly cultivated for the blue coloring matter derived from its leaves.  See isatin.
 2. A blue dyestuff, or coloring matter, consisting of the powdered and fermented leaves of the Isatis tinctoria. It is now superseded by indigo, but is somewhat used with indigo as a ferment in dyeing.
    Their bodies . . . painted with woad in sundry figures.   --Milton.
 Wild woad Bot., the weld (Reseda luteola).  See Weld.
 Woad mill, a mill grinding and preparing woad.
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 woad
      n 1: a blue dyestuff obtained from the woad plant
      2: any of several herbs of the genus Isatis