Source : Webster's Revised Unabridged Dictionary (1913)

Vasodilator \Vas`o*di*lat"or\, a.[L. vas a vessel + dilator.]
   (Physiol.)
   Causing dilation or relaxation of the blood vessels; as, the
   vasodilator nerves, stimulation of which causes dilation of
   the blood vessels to which they go. These nerves are also
   called {vaso-inhibitory}, and {vasohypotonic} nerves, since
   their stimulation causes relaxation and rest.

Source : WordNet®

vasodilator
     n : a drug that causes dilation of blood vessels [syn: {vasodilative}]