The Collaborative International Dictionary of English v.0.48:

Dogwood \Dog"wood`\ (-w[oo^]d`), n. [So named from skewers
   (dags) being made of it. --Dr. Prior. See Dag, and
   Dagger.] (Bot.)
   The Cornus, a genus of large shrubs or small trees, the
   wood of which is exceedingly hard, and serviceable for many
   purposes.
   [1913 Webster]

   Note: There are several species, one of which, Cornus
         mascula, called also cornelian cherry, bears a red
         acid berry. Cornus florida is the flowering dogwood,
         a small American tree with very showy blossoms.
         [1913 Webster]

   Dogwood tree.
   (a) The dogwood or Cornus.
   (b) A papilionaceous tree (Piscidia erythrina) growing in
       Jamaica. It has narcotic properties; -- called also
       Jamaica dogwood.
       [1913 Webster]

WordNet (r) 3.0 (2006):

dogwood
    n 1: a tree of shrub of the genus Cornus often having showy
         bracts resembling flowers [syn: dogwood, dogwood tree,
         cornel]
    2: hard tough wood of any dogwood of the genus Cornus; resembles
       boxwood