Labarum

lab′a-rum, n. a Roman military standard adopted as the imperial standard after Const an tine's conversion. It bore the Greek letters XP (Chr), joined in a monogram, to signify the name of Christ: a similar ecclesiastical banner borne in proce ions: any moral standard or guide. [Late Gr. labaron , origin unknown. Some make bold to derive from Basque labaria , a standard.]