Xviii

Part of speech: noun

Definitions

1. The Roman numeral representing the number eighteen, written as the letters X, V and I together
2. A Roman numeral meaning eighteen, formed by placing ten, five and three single marks in sequence
3. The lowercase Roman numeral standing for the quantity eighteen in older numbering systems

Etymology: Xviii is the Roman numeral for 18, built from X (10), V (5), and three I's (1 each). Roman numerals had no zero and no place-value system, so each symbol simply adds or subtracts. The subtractive rule, where a smaller symbol before a larger one is subtracted, is why 18 is written XVIII rather than the longer XVVIII, and the same logic underlies IX for 9 and XC for 90. The "xviii" spelling is also used as a shorthand in writing, especially in lowercase, where it marks the eighteenth in a series such as a century, a royal name, or a volume number. In English it appears in phrases like "the xviii century" or in the names of monarchs and popes, which is why readers encounter it as a noun-like label. Because it is simply a numeral, there is no separate Latin or Greek word to trace beyond the Roman system itself.