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

&fist; 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.