The Collaborative International Dictionary of English v.0.48:

Conium \Co*ni"um\ (? or ?), n. [NL., fr. Gr. ? hemlock.]
   1. (Bot.) A genus of biennial, poisonous, white-flowered,
      umbelliferous plants, bearing ribbed fruit ("seeds") and
      decompound leaves.
      [1913 Webster]

   2. (Med.) The common hemlock (Conium maculatum, poison
      hemlock, spotted hemlock, poison parsley), a roadside weed
      of Europe, Asia, and America, cultivated in the United
      States for medicinal purpose. It is an active poison. The
      leaves and fruit are used in medicine.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Conium
    n 1: small genus of highly toxic biennials: hemlock [syn:
         Conium, genus Conium]