Mid 17th century; earliest use found in John Spottiswood (1565–1639), archbishop of St Andrews and historian. From post-classical Latin legislatorius from classical Latin lēgislātor + -ius, suffix forming adjectives; compare -ory.
Definition of legislatory in US English:
legislatory
adjective
= legislatorial.
Origin
Mid 17th century; earliest use found in John Spottiswood (1565–1639), archbishop of St Andrews and historian. From post-classical Latin legislatorius from classical Latin lēgislātor + -ius, suffix forming adjectives; compare -ory.