[1] : 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
see also:
artemisia santonica chenopodium anthelminticum wormseed mustard erysinum cheiranthoides 

[2] : WordNet (r) 2.0

wormseed mustard
     n : slender yellow-flowered european mustard often troublesome
         as a weed; formerly used as an anthelmintic syn: erysimum
         cheiranthoides
see also:
erysimum cheiranthoides 

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