The Collaborative International Dictionary of English v.0.48:

Vincetoxin \Vin`ce*tox"in\, n. (Chem.)
   A glucoside extracted from the root of the white swallowwort
   (Vincetoxicum officinale, a plant of the Asclepias family)
   as a bitter yellow amorphous substance; -- called also
   asclepiadin, and cynanchin.
   [1913 Webster]