diaconicum

It corresponds to the secretarium or diaconicum of old.

The Catholic Encyclopedia, Volume 13: Revelation-Stock 1840-1916 1913

In large churches the diaconicum majus comprised several rooms: the salutatorium, for reception and audiences of the bishop; the thesaurarium, where sacred vessels and books were kept; and the diaconicum properly so called.

The Catholic Encyclopedia, Volume 4: Clandestinity-Diocesan Chancery 1840-1916 1913

Prothesis and diaconicum are ordinarily on either side of the apse.

The Catholic Encyclopedia, Volume 4: Clandestinity-Diocesan Chancery 1840-1916 1913

The diaconicum is distinct from the prothesis, a small room where the offerings of the people were received.

The Catholic Encyclopedia, Volume 4: Clandestinity-Diocesan Chancery 1840-1916 1913

The Council of Laodicea (can, xxi) forbade the inferior orders of the clergy to enter the diaconicum or touch the sacred vessels, and a canon of the first Council of Toledo pronounces that deacons who have been subjected to public penance must in future remain with the subdeacons and thus be withdrawn from the handling of these vessels.

The Catholic Encyclopedia, Volume 4: Clandestinity-Diocesan Chancery 1840-1916 1913

Possibly the Greek pastophorion, where the Holy Eucharist was reserved, was simply the diaconicum.

The Catholic Encyclopedia, Volume 4: Clandestinity-Diocesan Chancery 1840-1916 1913