xiii
num. B2 Upper Intermediate xi·ii
num. the number thirteen written in Roman numerals. You see this in history books, on old clocks, or in the names of kings.
num. the cardinal number thirteen expressed in Roman notation. Often used in historical contexts, such as the names of monarchs or centuries.
The chapter ends on page xiii of the introduction.
King Louis XIII of France ruled during the early seventeenth century.
The document was dated with the Roman numeral XIII to signify the thirteenth day of the month, a common practice in formal historical records.
Usage
Typically used as a label or ordinal marker rather than for mathematical calculations.