pyx
(Greek: pyxos, box-tree)
A vessel in which the Sacred Host is either preserved or carried.
It is made of precious metal, gold or silver, and if made of silver, is usually gold-plated.
The pyx, or ciborium, is the ordinary receptacle for the preservation of the Sacred Host in the tabernacle.
A smaller pyx is used for carrying the Blessed Sacrament to the sick.
This is a small round case and should be gold-plated at least inside.
It suffices for from one to four or five hosts.
New Catholic Dictionary