Antimensium

ANTIMENSIUM, an´´ti-men´si-um: A name applied in the Greek Church to a linen cloth spread upon the altar before the beginning of the eucharistic service, and considered as making it an altar ready for the sacrifice. Since the Greek Church, like the Roman Catholic, holds that the eucharistic sacrifice may be offered only on a consecrated altar, and since this consecration can be performed only by the bishop (taking place usually at the time of the consecration of the church), the mass could not be celebrated in churches not yet consecrated, if the use of this consecrated cloth—in the Roman Catholic Church, of a portable altar-stone (see Altar)—were not held to supply the deficiency.

(Georg Rietschel).