Wafer

A thin cake made of flour and other ingredients.

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.

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

To seal or close with a wafer.