Labarum n. : The standard adopted by the Emperor Constantine after his conversion to Christianity. It is described as a pike bearing a silk banner hanging from a crosspiece, and surmounted by a golden crown. It bore a monogram of the first two letters (CHR) of the name of Christ in its Greek form. Later, the name was given to various modifications of this standard.

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Taxonomy
labarum, Constantine, Chi-Rho, the cross, Rho symbol, cross, the Christian, battle, evidence, Life of Constantine, emperor, the emperor Constantine, Eusebius of Caesarea, Licinius, army, soldiers, the sign, labara.

Defination from the web:
labarum (Greek: λάβαρον) was a vexillum (military standard) that displayed the "Chi-Rho" symbol, formed from the first two Greek letters of ... The emperor Constantine Monomachos (centre panel of a Byzantine enamelled crown) holding a miniature labarum ...