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):

Helleborus niger
    n 1: European evergreen plant with white or purplish rose-like
         winter-blooming flowers [syn: Christmas rose, winter
         rose, black hellebore, Helleborus niger]