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Why is a 14-day period called a fortnight?
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First complete printed title page for the Kalendarium (“Calendar”) by Regiomontanus, 1476.
The term "fortnight" is a contraction of the Middle English fourtenight, which itself evolved from the Old English fēowertīene niht, meaning "fourteen nights."1
In the context of chronology, this term reflects an ancient method of measuring time by counting nights rather than days, a practice common in various early cultures. A fortnight represents a period of exactly 14 days, or two weeks.1