• Happening every two weeks.
  • Happening twice a week; semiweekly.

  • occurring twice a week
  • occurring every two weeks fortnightly

  • Occurring once every two weeks.
  • Occurring twice a week

Here is the bottom line:
The prefix bi- applies to the week rather than to the events that occur, therefore giving the sense of “every two weeks”. But in the UK is means “twice a week”.

For the sake of clarity, it is advisable to use one of the synonyms instead.


  • Every two weeks: fortnightly
  • Twice a week: twice-weekly, semiweekly

Am I seriously going to start saying fortnightly???


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