Undecimber

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Undecimber is a rare term used in computer science, and specifically in the programming language Java, as the name of a 13th month in a calendar. Although the Gregorian calendar used in most parts of the world includes only 12 months, there exist some lunar calendars that are divided into 13 sidereal months. Another example is the Hebrew calendar, in which approximately 40% of all years have 13 months. In case a computer program is intended to carry out date computations in such a calendar, support for 13-month years and the name Undecimber have been introduced into Java.

Some confusion surrounds the term since many people at first sight consider it nonsensical to talk about 13 months in a year. However, the month Undecimber is well-defined and has a purpose as stated above, even if it is infrequently used.

The word “Undecimber” itself is based on the Latin word “undecim,” meaning “eleven.” This is intended as a continuation to “December,” which derives from “decem,” meaning “ten.” The “i” in Undecimber is therefore correct, even though “December” is spelled with an “e” in that place.