The Collaborative International Dictionary of English v.0.48:

dyer's broom \dyer's broom\, dyer's-broom \dyer's-broom\n.
   small Eurasian shrub (Genista tinctoria) having clusters of
   yellow flowers that yield a dye; common as weed in England
   and U.S.; sometimes grown as an ornamental.

   Syn: woodwaxen, dyer's greenweed, dyer's weed, dyer's rocket,
        dyeweed, greenweed, whin, woadwaxen, Genista
        tinctoria.
        [WordNet 1.5]