Undecimber or Undecember is a name for a thirteenth month in a calendar that normally has twelve months.

Etymology

The word ''undecimber'' is based on the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word ''undecim'' meaning "eleven". It is formed in analogy with ''

December December is the twelfth and final month of the year in the Julian and Gregorian calendars. Its length is 31 days. December's name derives from the Latin word ''decem'' (meaning ten) because it was originally the tenth month of the year in t ...

,'' which, though the twelfth month in the

Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...

, derives from ''decem'' meaning "ten". The

Oxford Latin Dictionary The ''Oxford Latin Dictionary'' (or ''OLD'') is the standard English lexicon of Classical Latin, compiled from sources written before AD 200. Begun in 1933, it was published in fascicles between 1968 and 1982; a lightly revised second edition ...

defines it as "a humorous name given to the month following December".

Roman use

Some modern authors, including the World Calendar Association and

Isaac Asimov Isaac Asimov ( ; – April 6, 1992) was an Russian-born American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. H ...

. have reported the names "Undecember" and "Duodecember" for the two intercalary months inserted between November and December upon the adoption of the

Julian calendar The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts ...

in 44 BC. This claim has no contemporary evidence;

Cicero Marcus Tullius Cicero ( ; ; 3 January 106 BC – 7 December 43 BC) was a Roman statesman, lawyer, scholar, philosopher, orator, writer and Academic skeptic, who tried to uphold optimate principles during the political crises tha ...

refers to the months as "''intercalates prior'' and ''intercalates posterior"'' in his letters. Historian

Cassius Dio Lucius Cassius Dio (), also known as Dio Cassius ( ), was a Roman historian and senator of maternal Greek origin. He published 80 volumes of the history of ancient Rome, beginning with the arrival of Aeneas in Italy. The volumes documented the ...

tells that Licinus, procurator of

Gaul Gaul () was a region of Western Europe first clearly described by the Roman people, Romans, encompassing present-day France, Belgium, Luxembourg, and parts of Switzerland, the Netherlands, Germany, and Northern Italy. It covered an area of . Ac ...

, added two months to the year 15 BC, because taxes were paid by the month. Dio, who wrote in

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

, says Licinus "called he added monthsthe eleventh and the twelfth";

August Immanuel Bekker August Immanuel Bekker (21 May 17857 June 1871) was a German philologist and critic. Biography Born in Berlin, Bekker completed his classical education at the University of Halle under Friedrich August Wolf, who considered him as his most promi ...

suggested the Latin names might have been "Undecember" and "Duodecember". The abbreviation ''Unde'' appears in a Roman

inscription Epigraphy () is the study of inscriptions, or epigraphs, as writing; it is the science of identifying graphemes, clarifying their meanings, classifying their uses according to dates and cultural contexts, and drawing conclusions about the wr ...

from Vercellae in

Cisalpine Gaul Cisalpine Gaul (, also called ''Gallia Citerior'' or ''Gallia Togata'') was the name given, especially during the 4th and 3rd centuries BC, to a region of land inhabited by Celts (Gauls), corresponding to what is now most of northern Italy. Afte ...

, dating between the first century BC and the first century AD.

Computing

In the

Java Platform, Standard Edition Java Platform, Standard Edition (Java SE) is a computing platform for development and deployment of porting, portable code for desktop computer, desktop and server (computing), server environments. Java SE was formerly known as Java 2 Platform, S ...

, the java.util.Calendar

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

includes support for calendars which permit thirteen months. Although the

used in most parts of the world includes only twelve months, there exist some

lunar calendar A lunar calendar is a calendar based on the monthly cycles of the Moon's phases ( synodic months, lunations), in contrast to solar calendars, whose annual cycles are based on the solar year, and lunisolar calendars, whose lunar months are br ...

s that are divided into

synodic month In lunar calendars, a lunar month is the time between two successive Syzygy (astronomy), syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona people, S ...

s, with an intercalary or "leap" month added in some years. For example, in the

Hebrew calendar The Hebrew calendar (), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance and as an official calendar of Israel. It determines the dates of Jewish holidays and other rituals, such as '' yahrze ...

seven years out of every nineteen (37%) have the "embolismic month" Adar I. The constant java.util.Calendar.UNDECIMBER represents such a month.

Accounting

In accounting, a thirteenth month is sometimes used to adjust financial statements for an entire year without affecting monthly results. For example, an organization may wish to adjust its books to reflect the fact that some of its sales and resulting payments due from customers will not be paid. If an organization only does this once per year the organization can attribute these adjustments to "Month 13" so as not to inaccurately post a full year's worth of write offs to one month.

References

External links