Mid 19th century; earliest use found in The Southern Quarterly Review. From postillate + -ion; compare -ation. Compare post-classical Latin postillatio commenting.
Definition of postillation in US English:
postillation
noun
The writing of postils; preaching from postils.
Origin
Mid 19th century; earliest use found in The Southern Quarterly Review. From postillate + -ion; compare -ation. Compare post-classical Latin postillatio commenting.