The Collaborative International Dictionary of English v.0.48:

Wormwood \Worm"wood\, n. [AS. werm?d, akin to OHG. wermuota,
   wormuota, G. wermuth, wermut; of uncertain origin.]
   [1913 Webster]
   1. (Bot.) A composite plant (Artemisia Absinthium), having
      a bitter and slightly aromatic taste, formerly used as a
      tonic and a vermifuge, and to protect woolen garments from
      moths. It gives the peculiar flavor to the cordial called
      absinthe. The volatile oil is a narcotic poison. The term
      is often extended to other species of the same genus.
      [1913 Webster]

   2. Anything very bitter or grievous; bitterness.
      [1913 Webster]

            Lest there should be among you a root that beareth
            gall and wormwood.                    --Deut. xxix.
                                                  18.
      [1913 Webster]

   Roman wormwood (Bot.), an American weed (Ambrosia
      artemisiaefolia); hogweed.

   Tree wormwood (Bot.), a species of Artemisia (probably
      Artemisia variabilis) with woody stems.

   Wormwood hare (Zool.), a variety of the common hare (Lepus
      timidus); -- so named from its color.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Roman wormwood
    n 1: European wormwood; minor source of absinthe [syn: Roman
         wormwood, Artemis pontica]
    2: glaucous herb of northeastern United States and Canada having
       loose racemes of yellow-tipped pink flowers; sometimes placed
       in genus Fumaria [syn: Roman wormwood, rock harlequin,
       Corydalis sempervirens, Fumaria sempervirens]