The Collaborative International Dictionary of English v.0.48:

Mezereon \Me*ze"re*on\, n. [F. m['e]z['e]r['e]on, Per.
   m[=a]zriy[=u]n.] (Bot.)
   A small European shrub (Daphne Mezereum), whose acrid bark
   is used in medicine.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Umbelliferone \Um`bel*lif"er*one\, n. (Chem.)
   A tasteless white crystalline substance, C9H6O3, found in
   the bark of a certain plant (Daphne Mezereum), and also
   obtained by the distillation of certain gums from the
   Umbelliferae, as galbanum, asafetida, etc. It is analogous
   to coumarin. Called also hydroxy-coumarin. Its strong
   fluorescence under ultraviolet light makes it useful in
   analytical biochemistry, as, for example, to detect
   phosphatase activity by hydrolysis of umbelliferyl phosphate.
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Daphnin \Daph"nin\, n. [Cf. F. daphnine.] (Chem.)
   (a) A dark green bitter resin extracted from the mezereon
       (Daphne mezereum) and regarded as the essential
       principle of the plant. [R.]
   (b) A white, crystalline, bitter substance, regarded as a
       glucoside, and extracted from Daphne mezereum and
       Daphne alpina.
       [1913 Webster]

WordNet (r) 3.0 (2006):

Daphne mezereum
    n 1: small European deciduous shrub with fragrant lilac-colored
         flowers followed by red berries on highly toxic twigs [syn:
         mezereon, February daphne, Daphne mezereum]