Source : Webster's Revised Unabridged Dictionary (1913)

Helleborein \Hel`le*bo"re*in\, n. (Chem.)
   A poisonous glucoside accompanying helleborin in several
   species of hellebore, and extracted as a white crystalline
   substance with a bittersweet taste. It has a strong action on
   the heart, resembling digitalin.