Source : Webster's Revised Unabridged Dictionary (1913)

Silkweed \Silk"weed`\, n. (Bot.)
   Any plant of the genera {Asclepias} and {Acerates} whose seed
   vessels contain a long, silky down; milkweed.

Source : WordNet®

silkweed
     n : any of numerous plants of the genus Asclepias having milky
         juice and pods that split open releasing seeds with downy
         tufts [syn: {milkweed}]