(As a mass noun) the plates, cups, and other vessels and utensils, typically of precious metal, used in the communion rite; (as a count noun) one of these, especially a communion plate.
Origin
Mid 17th century.
Definition of altar plate in US English:
altar plate
noun
(As a mass noun) the plates, cups, and other vessels and utensils, typically of precious metal, used in the communion rite; (as a count noun) one of these, especially a communion plate.