What is Postil?

Legal Definition
A postil or postill (Latin: postilla; German: Postille) was originally a term for Bible commentaries. It is derived from the Latin "post illa verba textus" (after these words), referring to Biblical readings. The word first occurs in the chronicle (with reference to examples of 1228 and 1238) of Nicolas Trivetus, but later it came to mean only homiletic exposition, and thus became synonymous with homily in distinction from the thematic sermon. Finally, after the middle of the fourteenth century, it was applied to an annual cycle of homilies.
-- Wikipedia
Legal Definition
Postillae. Marginal notes made in a book or writing for reference to other parts of the same, or some other book or writing.
-- Bouviers Law Dictionary