Dictionary:

jimsonweed

  (jĭm'sən-wēd')

A coarse poisonous plant (Datura stramonium) having large, trumpet-shaped white or purplish flowers and prickly capsules. Also called stramonium.

[Alteration of Jamestown weed, after JAMESTOWN, Virginia.]

Jamestown, the first English-speaking colony in North America, gave us the name of our first English-speaking hallucinogen. Commemorating what might be considered a colonial Woodstock is the name Jamestown weed, as described in a 1687 Letter from Mr. John Clayton...Giving an Account of Several Observables in Virginia. When certain soldiers "went to gather a Sallad," Mr. Clayton explains, "lighting in great Quantities on an Herb called James-town-weed, they gathered it; and by eating thereof in plenty, were rendered apish and foolish, as if they had been drunk, or were become idiots."

That this "James-town-weed" had unusual pharmacological properties was confirmed in a 1709 description: "The Seed it bears is very like that of an Onion; it is excellent for curing Burns, and asswaging Inflammations."

By the 1800s, the once prominent city of Jamestown was reduced to a few ruins, and Jamestown weed was likewise reduced to its present form, jimsonweed. A 1977 book of useful plants says jimsonweed "is extremely poisonous," but adds, "In Appalachia, poultices made of the leaves have been used to treat wounds and kill pains while in the Southwest it has been used as an hallucinogenic."

The noun has one meaning:

Meaning #1: intensely poisonous tall coarse annual tropical weed having rank-smelling foliage, large white or violet trumpet-shaped flowers and prickly fruits
  Synonyms: jimson weed, Jamestown weed, common thorn apple, apple of Peru, Datura stramonium