The Collaborative International Dictionary of English v.0.48:

Hellebore \Hel"le*bore\, n. [L. helleborus, elleborus, Gr. ?, ?;
   cf. F. hell['e]bore, ell['e]bore.]
   [1913 Webster]
   1. (Bot.) A genus of perennial herbs (Helleborus) of the
      Crowfoot family, mostly having powerfully cathartic and
      even poisonous qualities. Helleborus niger is the
      European black hellebore, or Christmas rose, blossoming in
      winter or earliest spring. Helleborus officinalis was
      the officinal hellebore of the ancients.
      [1913 Webster]

   2. (Bot.) Any plant of several species of the poisonous
      liliaceous genus Veratrum, especially Veratrum album
      and Veratrum viride, both called white hellebore.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hellebore
    n 1: perennial herbs of the lily family having thick toxic
         rhizomes [syn: hellebore, false hellebore]
    2: any plant of the Eurasian genus Helleborus