Tredecimus

Tredecimus is a Latin adjective and ordinal numeral meaning thirteenth. It functions to indicate position in a sequence and agrees with the noun it modifies in gender and number, with forms such as tredecimus (masculine nominative singular), tredecima (feminine), and tredecimum (neuter).

Etymology and formation: tredecimus is derived from tredecim, the cardinal for thirteen, and the standard Latin suffix -us for the masculine nominative singular. The construction follows the familiar pattern of Latin ordinals formed from cardinals, and it has corresponding feminine and neuter forms for use with different nouns.

Usage and context: In classical and medieval Latin, tredecimus is used in calendrical, legal, literary, and everyday enumerations to denote the thirteenth item in a series. It appears on calendars, in lists, and in textual passages that require an explicit ordinal position, for example on the thirteenth day (dies tredecimus) or as part of a numbered sequence.

Historical and related terms: The form is associated with compound or collective terms such as tredecimviri, a board of thirteen officials (for example, the tredecimviri sacris faciundis, a college responsible for sacred rites). Variants and alternate expressions for the thirteenth position appear in Latin literature, including occasional uses like tertius decimus or terdecimus in some late or emphatic contexts.

See also: Latin numerals; duodecimus (twelfth); undecimus (eleventh); tredecim (the cardinal thirteen). Tredecimus remains primarily of interest in historical Latin, paleography, and the study of Roman offices and calendars.