Source : Webster's Revised Unabridged Dictionary (1913)

Postillate \Pos"til*late\, v. t. [LL. postillatus, p. p. of
   postillare.]
   To explain by marginal notes; to postil.

         Tracts . . . postillated by his own hand. --C. Knight.

Postillate \Pos"til*late\, v. i.
   1. To write postils; to comment.

   2. To preach by expounding Scripture verse by verse, in
      regular order.