Source : Webster's Revised Unabridged Dictionary (1913)

Frostweed \Frost"weed`\, n. (Bot.)
   An American species of rockrose ({Helianthemum Canadense}),
   sometimes used in medicine as an astringent or aromatic
   tonic.

   Note: It has large yellow flowers which are often sterile,
         and later it has abundant but inconspicuous flowers
         which bear seed. It is so called because, late in
         autumn, crystals of ice shoot from the cracked bark at
         the root; -- called also frostwort.

Source : WordNet®

frostweed
     n 1: perennial of the eastern United States having early solitary
          yellow flowers followed by late petalless flowers;
          so-called because ice crystals form on it during first
          frosts [syn: {frost-weed}, {frostwort}, {Helianthemum
          canadense}, {Crocanthemum canadensei}]
     2: tall perennial herb having clusters of white flowers; the
        eastern United States [syn: {Virginia crownbeard}, {frost-weed},
         {Verbesina virginica}]