labarum
noun/ˈlæbəɹəm/
Etymology Borrowed from Latin labarum.
1
The Roman military standard adopted by Constantine I. The banner was known for its Christian chi-rho sign - ☧.
- 1658: Nor shall we urge the labarum, and famous Standard of Constantine, or make further use thereof, than as the first Letters in the Name of our Saviour Christ — Sir Thomas Browne, The Garden of Cyrus (Folio Society 2007, p. 168)