twentyfirst

Twentyfirst refers to the ordinal position of twenty-one, commonly written as twenty-first in standard English. The hyphenated form twenty-first is the conventional spelling when used as an adjective or in written references to the ordinal number. The unhyphenated form twentyfirst is rare and generally considered nonstandard, though it may appear in certain branding, domain names, or informal usage where punctuation and spacing are omitted.

Common uses of the twenty-first are in dating, ordering, and time-period designations. For example, the twenty-first of a month denotes a specific date, and the twenty-first item in a sequence identifies a particular position. In longer contexts, twenty-first is often used to describe modern eras, such as the twenty-first century, which spans from the year 2001 to 2100 in most conventional frameworks.

Notable terminology and references include the Twenty-First Amendment to the United States Constitution, which repealed Prohibition and was ratified in 1933. The phrase also appears in discussions of contemporary history and culture, where writers refer to the twenty-first century’s social, technological, and political developments. In editorial practice, hyphenation and capitalization follow standard style guides, with twenty-first treated as a compound adjective and capitalized in official titles, such as Twenty-First Amendment or Twenty-First Century studies.