*vasodilator*

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. [ 1913 Webster ]