Look up fortnight in Wiktionary, the free dictionary.
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. Some wages, salaries, and social security benefits are paid on a fortnightly basis; however in North America it is far more common to use the term biweekly. Note that neither of these terms should not be confused with semimonthly, which results in 24 pay periods (12 months × 2), instead of the 26 (52 weeks ÷ 2) of fortnightly/biweekly.
In many languages there is no single word for a two-week period, and the equivalent terms "two weeks", "14 days" or "15 days" (counting inclusively) have to be 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.
Similarly in Greek the term δεκαπενθήμερο (dekapenthímero), meaning "15 days", is used.
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.