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A fortnight is a unit of time equal to 14 days (2 weeks). The word derives from the Old English: fēowertyne niht, meaning "fourteen nights". Fortnight and fortnightly are commonly used words in the English-speaking world, where some wages, salaries and social security benefits are paid on a fortnightly basis, except North America, where it is rare outside of some Canadian regions and insular traditional communities (e.g. Amish) in the United States. American and Canadian payroll systems may use the term biweekly in reference to pay periods every two weeks. Neither term should be confused with semimonthly (in one year there are 26 fortnightly or biweekly versus 24 semimonthly pay periods).
- For more information see eclipse cycle.
In astronomy, a fortnight is half a synodic month, the mean average time between a full moon and a new moon (and vice versa). This is equal to 14.77 days. In the Hindu calendar this period is called a Paksha (also Paksa) and consists of 15 Tithi.
In other languages
In many languages, there is no single word for a two-week period and the equivalents of "two weeks", "14 days" or (counting inclusively) "15 days" have to be used.
Among the Romance languages, there are the terms quincena (or quince días) in Spanish and Galician, quinzena (Portuguese and Catalan), quindicina (Italian), quinze jours or quinzaine (French), and chenzinǎ (Romanian), all meaning "15 days"; there are also the terms "bisettimanale" in Italian, "bisemanal" in Spanish, "bissemanal" in Portuguese, "bisetmanal" in Catalan, "bihebdomadaire" in French, and "bisǎptǎmânal" in Romanian, that literally mean biweekly.
Similarly, in Greek, the term δεκαπενθήμερο (dekapenthímero), meaning "15 days", is also used.
Celtic languages: in Welsh, the term pythefnos, meaning "15 nights", is used instead. This is in keeping with the Welsh term for a week, which is wythnos ("eight nights"). In Irish, the term is coicís.
Semitic languages have a special "doubling suffix"; when added at the end of the word for "week", it changes the meaning to "two weeks". In Hebrew, the single-word שבועיים (shvu′ayim) means exactly "two weeks". Also in Arabic, by adding the common dual suffix to the word for week, أسبوع, the form أسبوعين (usbu′ayn), meaning "two weeks", is formed.
- The Concise Oxford Dictionary, 5th Edition, 1964, p. 480
- Senight, sennight or se'night (seven-night), an old word for the week, was still in use in the early 19th century, to judge from Jane Austen's letters.
- "Australian Government - How much Disability Support Pension do I get?". Archived from the original on 2008-04-16. Retrieved 2008-05-22.
- Littmann, Mark; Fred Espenak; Ken Willcox (2008). Totality: Eclipses of the Sun. Oxford University Press. ISBN 0-19-953209-5.
- Synodic Month definition Eric W. Weisstein