The Collaborative International Dictionary of English v.0.48:

Swallowwort \Swal"low*wort`\, n. (Bot.)
      (a) See Celandine.
      (b) A poisonous plant (Vincetoxicum officinale) of the
          Milkweed family, at one time used in medicine; -- also
          called white swallowwort.
          [1913 Webster]

   African swallowwort, a plant of the genus Stapelia.
      [1913 Webster]

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]