21st

21st is the ordinal indicator for the number 21 in English. It denotes the twenty-first item in a sequence and is written as 21st. In English, ordinals ending in 1 typically take the suffix “st” (1st, 21st, 31st), while numbers ending in 11, 12, or 13 use “th” (11th, 12th, 13th) due to a historical exception. The form 21st is used in dates, rankings, and enumerations, and can appear in street names or formal titles. In plain text, ordinals are commonly written as 21st, though typographic practice sometimes uses superscripts.

Common usages include indicating the position of something in a sequence (the 21st item), marking dates (the 21st of May), and naming streets or districts (21st Street). The 21st ordinal is encountered in education, publishing, and media when listing elements in order or referring to specific moments in time.

The 21st century refers to the period from January 1, 2001, to December 31, 2100. The designation is used in historical, cultural, and geopolitical contexts to frame events within that century. Century labels are ordinal descriptors tied to a roughly two-century span and are distinct from the numerical year or decade.

Notable uses of the term include the 21st Amendment to the United States Constitution, ratified in 1933, which repealed Prohibition. The phrase also appears in various institutional names, publications, and geographic designations that use ordinal labeling. Related topics include the 21st century and other ordinals such as 22nd or 23rd.