The Collaborative International Dictionary of English v.0.48:

Isatis \I"sa*tis\ (?; 277), n. [L., a kind of plant, Gr. ?
   woad.] (Bot.)
   A genus of herbs, some species of which, especially the
   Isatis tinctoria, yield a blue dye similar to indigo; woad.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Isatis
    n 1: Old World genus of annual to perennial herbs: woad [syn:
         Isatis, genus Isatis]