What is 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 called?

wafer — (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. (Webster's 1913.)

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