eighteenth

Eighteenth is the ordinal form of the cardinal number eighteen. It is used to indicate a position in a sequence, such as the eighteenth item in a list, the eighteenth chapter of a book, or the eighteenth street on a grid. It can also function as a noun when referring to a fraction, with "an eighteenth" or "one eighteenth" meaning 1/18, though this usage is less common in everyday speech.

The word derives from the number eighteen, with the ordinal suffix formed by replacing the final -teen with -teenth, giving eighteenth. This follows the general English pattern for ordinals of numbers ending in -teen, such as seventeenth and nineteenth.

In historical and cultural contexts, "the eighteenth century" denotes the time spanning roughly the years 1701 through 1800 under the common convention. In American history, the Eighteenth Amendment to the United States Constitution, ratified in 1919 and in effect from 1920 to 1933, established nationwide Prohibition and was repealed by the Twenty-first Amendment.

The eighteenth letter of the Latin alphabet is R, when counting from A as the first letter. In other uses, "eighteenth" appears in legal, scientific, and mathematical language to denote order, editions, or divisions.

Overall, eighteenth functions as a standard ordinal descriptor across language, time, and formal documentation, parallel to its cardinal counterpart eighteen.