Ciborium: from the Greek word pyxis (=box, casket), a Ciborium is a cup-shaped vessel with an arched cover used to hold  the consecrated Hosts during the Eucharistic celebration which are then  stored  in the tabernacle for communion to the sick, the viaticum to the dying and for Eucharistic adoration.

A Ciborium is also called a Pyx or Pix, the latter is more aptly applied to the small round metal case used to safely and properly carry the Eucharist to the sick and homebound.