xviii
n. C2 Proficiency xvi·ii
n. the number eighteen written in Roman numerals. You use this when you want to write a date or a chapter number in an old style.
n. the Roman numeral representing the cardinal number eighteen.
The historian noted that the treaty was signed on the eighteenth day of the month, written as XVIII.
While modern digital clocks use Arabic numerals, many formal invitations still feature the date written in Roman numerals, such as the eighteenth of May as XVIII.