Commonly Confused Words: Biweekly vs. Fortnightly vs. Semi-weekly

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What does each word mean?

Biweekly means both ‘every two weeks’ and ‘twice a week’.

Click here for the full Spellzone dictionary definition of the word.

Here is biweekly used in some example sentences:

  • The club meets biweekly on Mondays and Thursdays.
  • The paper is distributed biweekly, usually in the second and fourth week of the month. 

Fortnightly is a British English word meaning ‘every two weeks’. 

Click here for the full Spellzone dictionary definition of the word.

Here is fortnightly used in an example sentence:

  • The paper is distributed fortnightly, usually in the second and fourth week of the month. 

Semi-weekly is a North American word meaning ‘twice a week’. 

Click here for the full Spellzone dictionary definition of the word.

Here is semi-weekly used in an example sentence:

  • The club meets semi-weekly on Mondays and Thursdays.

Where does each word come from? 

The word week comes from the Old English ‘wucu’ and the adverb weekly has been used in English since the fifteenth century. Semi-weekly dates to 1791 (the prefix semi- meaning ‘half’) and biweekly to 1865 (the prefix bi- meaning ‘two’). 

Fortnight is a seventeenth-century contraction of the Middle English ‘fourteniht’, from the Old English ‘feowertyne nigt’ meaning ‘fourteen nights’. 

Are there any tricks to help me remember the difference between biweekly, fortnightly, and semi-weekly?

  • Use the b in biweekly to remind you that the word means both ‘twice a week’ and ‘every two weeks’. 
  • Use the for in fortnight to remind that the word means ‘every fourteen days’. 
  • Remember that semi means half and think of the word as meaning ‘every half a week'.

Where can I find other posts about easy-to-confuse words?

Sources: The Online Etymology Dictionary


20 May 2019
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One of the students has put in a huge amount of effort in completing Spellzone at least 3 times a week since his arrival with us in January. Looking at his scores after the latest GL testing, his standardised score has risen from 99 to 131. This is a truly phenomenal result. I just wanted to share the best result I have ever seen.

Terrie Penrose-Toms, Casterton College

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