chrismon

noun

1. A Christogram.

   “The sacred monogram or chrismon was extensively used by Constantine […] a crown of gold, enclosing the chrismon or mysterious monogram”

2. A stylised siglum or character interpreted as an invocation of Christ in Merovingian and Carolingian documents.

   “The document usually begins with a verbal invocation (such as In Dei nomine, amen) or a chrismon (often Christ's monogram formed from the letters XP)”

3. A Christmas decoration with explicitly Christian religious symbolism.

   “Chrismons were first made as tree decorations by members of the Lutheran Church of the Ascension, Daville, Va., in 1957.”