in the Roman Catholic church and some other churches, a vessel in which the eucharistic host is carried in processions and is exposed during certain devotional ceremonies. Both names are derived from Latin words (monstrare and ostendere) that mean "to show." First used in France and Germany in the 14th century, when popular devotion to the Blessed Sacrament developed, monstrances were modeled after pyxes or reliquaries, sacred vessels for transporting the host or relics. The host was shown in a glass cylinder mounted on a base and surmounted by some sort of metal crown. In the 16th century the monstrance took its present shape: a circular pane of glass set in a cross or surrounded with metal rays. The host is placed in a holder called a lunette, which fits into an opening behind the glass.
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