Sentence:  The <WSD>luna</WSD>, which is a piece of glass in the shape of a moon, contains the Blessed Sacrament, previously consecrated. The <WSD>luna</WSD> is then placed in the middle of the sunburst of the monstrance. 
Meaning of the word marked with <WSD> tags:  A '''lunette''': a crescent-shaped receptacle, often glass, for holding the (consecrated) host (the bread of communion) upright when exposed in the monstrance. (from 19th c.)<ref>“[http://books.google.com/books?id=y_RpbmWNfHcC&pg=PA314&dq=luna luna]” in Don S. Armentrout and Robert Boak Slocum (editors), "An Episcopal Dictionary of the Church: A User-Friendly Reference for Episcopalians", Church Publishing, Inc. (2000), (978-0-89869-211-2).</ref>