The Collaborative International Dictionary of English v.0.48:

Offertory \Of"fer*to*ry\, n.; pl. Offertories . [L.
   offertorium the place to which offerings were brought, in LL.
   offertory: cf. F. offertoire.]
   1. The act of offering, or the thing offered. [Obs. or R.]
      --Bacon. --Bp. Fell.
      [1913 Webster]

   2. (R. C. Ch.)
      (a) An anthem chanted, or a voluntary played on the organ,
          during the offering and first part of the Mass.
      (b) That part of the Mass which the priest reads before
          uncovering the chalice to offer up the elements for
          consecration.
      (c) The oblation of the elements.
          [1913 Webster]

   3. (Ch. of Eng. & Prot. Epis. Ch.)
      (a) The Scripture sentences said or sung during the
          collection of the offerings.
      (b) The offerings themselves.
          [1913 Webster]