The Collaborative International Dictionary of English v.0.48:

Wormseed \Worm"seed`\, n. (Bot.)
   Any one of several plants, as Artemisia santonica, and
   Chenopodium anthelminticum, whose seeds have the property
   of expelling worms from the stomach and intestines.
   [1913 Webster]

   Wormseed mustard, a slender, cruciferous plant (Erysinum
      cheiranthoides) having small lanceolate leaves.
      [1913 Webster]

WordNet (r) 3.0 (2006):

wormseed
    n 1: rank-smelling tropical American pigweed [syn: American
         wormseed, Mexican tea, Spanish tea, wormseed,
         Chenopodium ambrosioides]