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Webster 1913 Edition

Noun.

[

Xylo-

+ Gr.

ὀστέον

bone.]

(Chem.)

A glucoside found in the poisonous berries of a species of honeysuckle (

Lonicera xylosteum

), and extracted as a bitter, white, crystalline substance.

xylostein ‎(uncountable)

A bitter principle obtained from the berries of the fly honeysuckle (Lonicera xylosteum) and formerly used in medicine.
- 2008, Alexander Campbell, Michael Chapman, Handbook of Poisoning in Dogs and Cats
  Honeysuckle fruits contain valerianic acid and xylostein, which are irritant.