'vasodilatory' originates from the combining form 'vaso-' (from Latin 'vas', meaning 'vessel') and 'dilatory' ultimately from Latin 'dilatare' meaning 'to spread out, expand'.

'vasodilatory' developed in modern medical English from earlier formations such as New Latin/English 'vasodilator' and 'vasodilation'; the noun and verb forms ('vasodilation', 'vasodilate') preceded adjectival uses like 'vasodilatory'.

Initially it referred specifically to the action of widening vessels ('relating to dilation of vessels'); it has remained consistent, denoting an agent or property that causes vessel widening.