{{Short description|13th month}}
{{wiktionarypar|decem|undecim}}
'''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 word ''undecim'' meaning "eleven". It is formed in analogy with ''December,'' which, though the twelfth month in the Gregorian calendar, derives from ''decem'' meaning "ten". The Oxford Latin Dictionary defines it as "a humorous name given to the month following December".<ref name="OLD Undecember">{{cite book |last=Glare |first=P.G. |title=Oxford Latin Dictionary |publisher=Clarendon Press |date=2002 |isbn=0-19-864224-5 }}</ref>
== Roman use ==
Some modern authors, including the World Calendar Association<ref>{{cite journal |date=1937 |journal=Journal of Calendar Reform |publisher=World Calendar Association |location=New York City |volume=7 |pages=64 |title=Why the World Needs This Reform |first=Jules |last=Jézéquel }}</ref> and Isaac Asimov<ref>{{cite book |last=Asimov |first=Isaac |author2=John Bradford |title=The clock we live on |publisher=Abelard-Schuman |date=1965 |edition=revised |page=125 |url=https://archive.org/details/clockweliveon00asim/page/125 |isbn=0-200-71100-8 }}</ref> have reported the names "Undecember" and "Duodecember" for the two intercalary months inserted between November and December upon the adoption of the Julian calendar in 44 BC. This claim has no contemporary evidence;{{cn|date=April 2025}} Cicero refers to the months as "''intercalates prior'' and ''intercalates posterior"'' in his letters.<ref>{{cite book |last=Heiland |first=W.E. |title=The Roman Republic |publisher=Cambridge University Press |location=Cambridge |date=1909 |volume=3 |page=347 §1269 |chapter=Chap LVIII: From the Battle of Thapsus to the Death of Caesar: 46–44 B.C. |chapter-url=https://archive.org/details/romanrepubli03heituoft/page/347 }}</ref>
Historian Cassius Dio tells that Licinus, procurator of Gaul, added two months to the year 15 BC, because taxes were paid by the month.<ref name="Cary335">{{cite book |author=Cassius Dio |author-link=Cassius Dio |translator=Earnest Cary |title=Roman History, vol VI |publisher=Harvard University Press |date=1917 |series=Loeb Classical Library |volume=83 |page=335, LIV 21.5 and note 2 |chapter=Book LIV |chapter-url=https://archive.org/details/dios-roman-history.-vol.-6-loeb-83/page/n171 }}</ref> Dio, who wrote in Greek, says Licinus "called [the added months] the eleventh and the twelfth"; August Immanuel Bekker suggested the Latin names might have been "Undecember" and "Duodecember".<ref name="Cary335"/> The abbreviation ''Unde'' appears in a Roman inscription from Vercellae in Cisalpine Gaul, dating between the first century BC and the first century AD.<ref>{{AE|1989|331}}, dating an event to the eleventh day before the Kalends of Undecember. In the Julian Calendar this corresponds to December 22; in the pre-Julian calendar, with twenty-nine days in December, it would have been December 20.</ref><ref name="OLD Undecember"/>
==Computing== In the Java Platform, Standard Edition, the <code>java.util.Calendar</code> class includes support for calendars which permit thirteen months.<ref name="On Java"> {{cite web |url=http://www.onjava.com/pub/a/onjava/2003/06/05/java_calendar.html |title=Making Sense of Java's Dates |access-date=2007-12-13 |first=Philipp K. |last=Janert |date=2007-06-04 |publisher=O'Reilly Media |work=On Java}}</ref> Although the Gregorian calendar used in most parts of the world includes only twelve months, there exist some lunar calendars that are divided into synodic months, with an intercalary or "leap" month added in some years. For example, in the Hebrew calendar seven years out of every nineteen (37%) have the "embolismic month" Adar I.<ref name="On Java"/><ref name="Mi Yodeya StackExchange">{{cite web |url=https://judaism.stackexchange.com/questions/37308/in-a-leap-year-is-the-extra-month-adar-i-or-adar-ii |title=In a leap year, is the extra month Adar I or Adar II? |work=Mi Yodeya StackExchange}}</ref> The constant <code>java.util.Calendar.UNDECIMBER</code> represents such a month.<ref>{{cite news|url=http://java.sun.com/javase/6/docs/api/java/util/Calendar.html#UNDECIMBER |title=java.util Class Calendar: UNDECIMBER |date=2008 |work=Java Platform, Standard Edition 6: API Specification |publisher=Sun Microsystems |access-date=2009-05-22 }}</ref>
==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.<ref>{{cite book |author-last1=L. Evans |author-first1=Denise L. |author-last2= Evans|author-first2=William |title=The Complete Real Estate Encyclopedia |date=2023 |publisher=The McGraw-Hill Companies, Inc. |url=https://financial-dictionary.thefreedictionary.com/thirteenth-month+accounting+period |access-date=7 Aug 2023}}</ref>
== See also == {{div col|colwidth=18em}} * 4–4–5 calendar * Accounting period * December 32 * February 29 * Mercedonius * Ophiuchus (astrology) {{end div col}}
== References == {{reflist}}
Category:13 (number) Category:Months Category:Latin words and phrases Category:Java (programming language) libraries