n 1 a  :  any herb of the genus Helleborus  b  :  the dried roots and rhizome of any medicinal herb of the genus Helleborus (as black hellebore H. niger or green hellebore H. viridis) or a powder or extract of this used by the ancient Greeks and Romans in treating mental and other disorders  2 a  :  any of several poisonous herbs of the genus Veratrum  b  :  the dried rhizome and roots of either of two hellebores of the genus Veratrum (the false hellebore V. viride of America and V. album of Europe) or a powder or extract of this containing alkaloids (as protoveratrine) used as a cardiac and respiratory depressant and also as an insecticide - called also veratrum , white hellebore  .
 
   
 
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