The Collaborative International Dictionary of English v.0.48:

Woad-waxen \Woad"-wax`en\, n. [Cf. Wood-wax.] (Bot.)
   A leguminous plant (Genista tinctoria) of Europe and
   Russian Asia, and adventitious in America; -- called also
   greenwood, greenweed, dyer's greenweed, and whin,
   wood-wash, wood-wax, and wood-waxen.
   [1913 Webster]

WordNet (r) 3.0 (2006):

woadwaxen
    n 1: small Eurasian shrub having clusters of yellow flowers that
         yield a dye; common as a weed in Britain and the United
         States; sometimes grown as an ornamental [syn: woodwaxen,
         dyer's greenweed, dyer's-broom, dyeweed, greenweed,
         whin, woadwaxen, Genista tinctoria]