Definition of wafer

• n. - A thin cake made of flour and other ingredients.
• n. - 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.
• n. - An adhesive disk of dried paste, made of flour, gelatin, isinglass, or the like, and coloring matter, -- used in sealing letters and other documents.
• v. t. - To seal or close with a wafer.