Definition of postil:
(n) :
A short homily or commentary on a passage of Scripture.
(n) :
A collection of homilies.
(n) :
(archaic) A Bible commentary written in its margins.
(n) :
A marginal note.
(v) :
(transitive) To write marginal or explanatory notes on; to gloss.
(v) :
(intransitive) To write postils, or marginal notes; to comment; to postillate.