POSTIL, or APOSTIL, properly a gloss on a scriptural text, particularly on a gospel text, hence any explanatory note on other writings. The word is also applied to a general commentary, and also to a homily or discourse on the gospel or epistle appointed for the day. The word in Medieval Latin was postilla, and this has been taken to represent post ilia sc. verba textus, i.e. " after these words of the text " (see Du Cange, Glossarium, s.v. postillae), but the form " apostil " may point to the Latin appositum, placed near or next to.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)