IPA: //ɒˈstɛn.sə.ri.əm//
KK: /ɑˈstɛn.sə.ri.əm/
A special container used in the Roman Catholic Church to hold and display the Eucharist, often during religious ceremonies.
During the mass, the priest placed the Eucharist in the ostensorium for the congregation to see.
Ostensorium → It is formed from "ostendere" (meaning to show) and the suffix "-ium" (often used to denote a place or medium). The word refers to a place or medium for showing, particularly in a religious context, such as a vessel for displaying the Eucharist.
Think of 'showing' ('ostendere') something in a special place ('-ium') — that's why ostensorium means a place for showing.