Source : Webster's Revised Unabridged Dictionary (1913)

Wafer \Wa"fer\, v. t. [imp. & p. p. {Wafered}; p. pr. & vb. n.
   {Wafering}.]
   To seal or close with a wafer.

Wafer \Wa"fer\, n. [OE. wafre, OF. waufre, qaufre, F. qaufre; of
   Teutonic origin; cf. LG. & D. wafel, G. waffel, Dan. vaffel,
   Sw. v[*a]ffla; all akin to G. wabe a honeycomb, OHG. waba,
   being named from the resemblance to a honeycomb. G. wabe is
   probably akin to E. weave. See {Weave}, and cf. {Waffle},
   {Gauffer}.]
   1. (Cookery) A thin cake made of flour and other ingredients.

            Wafers piping hot out of the gleed.   --Chaucer.

            The curious work in pastry, the fine cakes, wafers,
            and marchpanes.                       --Holland.

            A woman's oaths are wafers -- break with making --B.
                                                  Jonson.

   2. (Eccl.) A thin cake or piece of bread (commonly
      unleavened, circular, and stamped with a crucifix or with
      the sacred monogram) used in the Eucharist, as in the
      Roman Catholic Church.

   3. An adhesive disk of dried paste, made of flour, gelatin,
      isinglass, or the like, and coloring matter, -- used in
      sealing letters and other documents.

Source : WordNet®

wafer
     n 1: a small adhesive disk of paste; used to seal letters
     2: a small thin crisp cake or cookie
     3: thin disk of unleavened bread used in a religious service
        (especially in the celebration of the Eucharist)