Undecimber
| Industry | Calendar systems |
|---|---|
Area served | Worldwide (conceptual) |
Key people | Isaac Asimov (mentioned) |
| Products | Conceptual calendar month |
Undecimber or Undecember refers to a hypothetical thirteenth month added to a calendar that typically consists of twelve months.
Etymology
The term undecimber originates from the Latin word undecim, which means "eleven." It was created by analogy with December, which, although the twelfth month in the Gregorian calendar, is derived from decem, meaning "ten." According to the Oxford Latin Dictionary, it is described as a "joking name assigned to the month following December."
Roman use
Certain contemporary writers, including the World Calendar Association and Isaac Asimov, have mentioned "Undecember" and "Duodecember" as titles for two additional months inserted between November and December after the introduction of the Julian calendar in 44 BC. Nevertheless, no primary sources confirm this; Cicero referred to these periods only as "intercalates prior and intercalates posterior."
The historian Cassius Dio notes that Licinus, who governed Gaul, added two extra months in 15 BC due to tax collection schedules. Dio records that Licinus named these months the eleventh and twelfth; based on this, scholar August Immanuel Bekker proposed their Latin designations might have been "Undecember" and "Duodecember." Additionally, the abbreviation Unde is found on a Roman inscription from Vercellae in Cisalpine Gaul, dated between the first century BC and first century AD, which references an event occurring in Undecember.
Computing
Within the Java Platform, Standard Edition, the java.util.Calendar class accommodates calendars containing thirteen months. Although the Gregorian calendar comprises twelve months, some lunar calendar systems incorporate an intercalary or leap month during specific years. For instance, the Hebrew calendar inserts an additional month called "embolismic month" or Adar I in seven out of every nineteen years (approximately 37%). The constant java.util.Calendar.UNDECIMBER is used to represent such a month.
Accounting
In financial accounting, a thirteenth month is employed to make year-end adjustments without skewing monthly figures. Companies may assign modifications—such as anticipated unpaid sales—to a "Month 13" period, preventing large write-offs from clustering in a single month and thereby promoting more precise financial statements.