xxi
n. C2 Proficiency xxi
n. the Roman numeral for the number twenty-one. You might see this in old books or on historical signs.
n. the Roman numeral representing the cardinal number twenty-one. Used primarily in historical, legal, or formal contexts.
The chapter is labeled as Chapter XXI.
The historian noted that the event occurred in the year XXI of the reign of the emperor.
The manuscript was dated to the year XXI, though modern scholars suggest the actual date may be several decades later due to the shifting calendar system.