What Is a Fortnight? Definition, Origin, and Usage

There’s a word that quietly separates British English from American English: fortnight. The answer is 14 days – two weeks – but the term carries centuries of linguistic history that explains its regional divide, and by the end you’ll know its definition, etymology, and cultural context.

Definition: A fortnight is 14 days (two weeks) ·
Etymology: From Old English “fēowertīene niht” (fourteen nights) ·
Primary usage: United Kingdom, Ireland, and Commonwealth countries

The table below pulls together the essential facts about a fortnight.

What is a fortnight in days?

A fortnight is a unit of time equal to 14 days – exactly two weeks. This definition is consistent across all major English dictionaries, including Merriam-Webster (the authoritative American dictionary), Dictionary.com (a leading online dictionary), and Collins Dictionary (a respected British reference).

How many days are in a fortnight?

• 14 days, no more, no less. The Merriam-Webster entry explicitly states “14 days” and “two weeks.”
• It’s a fixed duration — not tied to a specific calendar month or alignment.

Is a fortnight exactly two weeks?

Yes. The Oxford Learner’s Dictionaries (the academic English reference) confirms that a fortnight is “a period of two weeks.” The standard modern meaning is centered on duration, not a specific calendar start.

The implication: No matter where you read it, “fortnight” always means 14 days. The confusion is never about the length, only about the word’s regional familiarity.

Why do they call it a fortnight?

The answer lies in how early Germanic peoples counted time. Instead of counting days, they counted nights. The Etymonline (the etymology reference) traces the word to Old English fēowertīene niht, literally “fourteen nights.”

What is the Old English origin of fortnight?

• The term combines fēower (four) + tīene (teen) + niht (night).
• The Dictionary.com entry notes that it was first recorded before 1000 AD.
• A parallel term sennight (seven nights) once existed but fell out of use (Definitions.net, a dictionary aggregator).

How does “fourteen nights” become “fortnight”?

The Oxford Learner’s Dictionaries (the academic English reference) explains the evolution: Old English fēowertīene niht → Middle English fourteniht → modern fortnight. The Dictionary.com entry adds that the spelling reflects contraction rather than a compound with the prefix fort- meaning strong.

The pattern: English preserved a night-based time unit from Old English, while most other languages switched to day-based counting. That’s why “fortnight” feels archaic to some speakers — it’s a fossil of an older worldview.

Do Americans say “fortnight”?

Rarely. The Wiktionary entry labels the term “chiefly UK, Ireland, and Commonwealth” and “dated in North America.” The Dictionary.com entry notes that it’s still in use in Great Britain and some former British colonies.

Why is fortnight common in British English but not American?

• American English simplified many British terms after independence, and “two weeks” became the standard.
• The Merriam-Webster inclusion shows that American dictionaries recognize the word, but it’s rarely used in everyday U.S. speech.

What is the American equivalent of fortnight?

“Two weeks.” For example, an American would say “I’m going on vacation in two weeks” rather than “in a fortnight.” The Collins Dictionary American English entry still defines it the same way, but the label “chiefly British” is often implied.

The catch: Americans are not ignorant of the word — they just don’t use it. Dictionaries give it equal status, but usage drives the divide.

What is 15 days called?

There is no standard English term for 15 days. It’s simply “fifteen days” or “two weeks and one day.” The same applies to other non-standard intervals.

What is 20 days called?

No standard term exists. “Score of days” is an archaic phrase, but it’s not recognized in modern dictionaries. The Merriam-Webster entry for “fortnight” does not list any counterpart for 20 days.

What is 3 weeks called?

21 days is simply “three weeks.” Some languages have a word for a three-week period (e.g., French trois semaines), but English does not. The Wiktionary entry confirms that no equivalent to “fortnight” exists for other multiples.

The pattern: English has a specialized term only for 14-day periods. This highlights the cultural importance of the two-week cycle in British and Commonwealth traditions — from pay periods to vacation planning.

What is a fortnight slang?

Fortnight is not slang. It’s a standard English term in British and Commonwealth usage. The Oxford Learner’s Dictionaries (the academic English reference) lists it as a formal noun, not a colloquialism.

Is “fortnight” considered slang?

• No. Every major dictionary treats it as a standard vocabulary word.
• The Merriam-Webster entry includes no slang label.

What does “fortnightly” mean?

It means occurring every fortnight — i.e., every two weeks. For example, a “fortnightly magazine” is published twice a month. The Collins Dictionary entry includes this adverbial form.

The upshot: Despite its rare appearance in American pop culture, “fortnight” remains a formal, everyday term for millions of English speakers worldwide.

Expert perspectives on the fortnight

“Fortnight: a period of 14 days; two weeks.”

— Merriam-Webster (the authoritative American dictionary)

“The word comes from Old English fēowertīene niht, meaning fourteen nights.”

— Oxford Learner’s Dictionaries (the academic English reference)

“Fortnight is still in use in Great Britain and some former British colonies.”

— Dictionary.com (a leading online dictionary)

“The term is chiefly UK, Ireland, and Commonwealth; dated in North America.”

— Wiktionary (a collaborative dictionary)

For American readers, the choice between “fortnight” and “two weeks” is a cultural signal: using the former marks you as either a British English speaker or someone who enjoys archaic vocabulary. For British and Commonwealth users, the word is simply practical — it’s shorter than “two weeks” and embedded in everyday scheduling. The takeaway for anyone writing for an international audience: use “fortnight” only if you’re confident your readers are comfortable with it, or save it for the moment you want to sound a little old-world.

For a deeper look at the exact duration and historical background, you can read more about how long a fortnight is.

Frequently asked questions