a standard or banner carried in Christian religious processions
2.
the military standard bearing a Christian monogram used by Constantine the Great
Word origin
C17: from Late Latin, of obscure origin
labarum in American English
(ˈlæbərəm)
nounWord forms: pluralˈlabara (ˈlæbərə)
the royal cavalry standard carried before the Roman emperors in war, esp. that first carried by Constantine, the first emperor to adopt Christianity: it usually bore the first two letters (XP) of the Greek Christos (Christ)