Discover what a fortnight means in maths, see real-life examples, and get exam tips from Vedantu's experts. Start learning now! Fortnight refers to a two-week duration , often used in various contexts, such as planning holidays, scheduling events, or measuring time intervals. While less commonly used in American English, it remains a standard term in British English and other English-speaking countries. A fortnight is a period of fourteen days, or two weeks. Related words are fortnights and fortnightly. The word fortnight comes from the Middle English word fourteniht, which is a contraction of the Old English Definition of FORTNIGHT in the Definitions.net dictionary. Meaning of FORTNIGHT . What does FORTNIGHT mean ? Information and translations of FORTNIGHT in the most comprehensive dictionary definitions resource on the web.