A fortnight is a unit of time equal to 14 days (two weeks). The word derives from the Old English term fēowertīene niht, meaning "fourteen nights" (or "fourteen days", since the Anglo-Saxons counted by nights).[1][2]

Astronomy and tides

Further information: Eclipse cycle

In astronomy, a lunar fortnight is half a lunar synodic month, which is equivalent to the mean period between a full moon and a new moon (and vice versa). This is equal to 14.07 days.[3][4] It gives rise to a lunar fortnightly tidal constituent (see: Long-period tides).

Analogs and translations

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.

See also


  1. ^ "Fortnight". The Concise Oxford Dictionary (5th ed.). 1964. p. 480.
  2. ^ 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.
  3. ^ Littmann, Mark; Fred Espenak; Ken Willcox (2008). Totality: Eclipses of the Sun. Oxford University Press. ISBN 978-0-19-953209-4.
  4. ^ Weisstein, Eric W. "Synodic Month definition".
  5. ^ BBC (16 October 2014). "BBC Wales - Catchphrase". BBC Wales. Retrieved 18 November 2016. Wythnos is a week.
  6. ^ "Do You Know How to Say Fortnight in Different Languages?". www.indifferentlanguages.com.