Answer: An Old English Contraction

If you’d never given much thought to the word “fortnight”, an English word that denotes a length of fourteen days, it’d be easy to assume it has something to do with military history. After all, the word seems like a pretty straightforward contraction of “fort” and “night”.

The word is a contraction, but a very old one, and the “fort” portion of it has nothing to do with military outposts. Fortnight comes to us by way of the Old English term “fēowertȳne niht”, or “fourteen nights”, and over time simply became “fortnight”.

The word is old enough that we have no concrete records of when it first came into use, nor do we have any concrete indication of why, but it’s safe to assume that English needed a simple way to express a unit of time readily analogous to half a month. Thus fortnight was born.

Still in regular use in most of the English-speaking world today, the word has fallen largely out of favor in North America, with intervals of two week events (such as receiving a paycheck every two weeks) described as “biweekly”—a word we find a tad inelegant compared to “fortnightly”, since biweekly could be interpreted to mean every other week or twice a week, whereas fortnightly has a singular definition.