Source : Webster's Revised Unabridged Dictionary (1913)

Hawkweed \Hawk"weed`\ (-w[=e]d`), n. (Bot.)
   (a) A plant of the genus {Hieracium}; -- so called from the
       ancient belief that birds of prey used its juice to
       strengthen their vision.
   (b) A plant of the genus {Senecio} ({S. hieracifolius}).
       --Loudon.

Source : WordNet®

hawkweed
     n 1: any of various plants of the genus Pilosella
     2: any of numerous often hairy plants of the genus Hieracium
        having yellow or orange flowers that resemble the
        dandelion