Just say what you mean:
“every 2 weeks,” or
“twice a week.”
Pick the one you mean.
Because unfortunately “biweekly” can mean either of those things, which kinda makes the word useless.
I only use it when referring to bi(sexual)weekly.
Get out of my head
The team I was on at work number of years ago had to hash this exact thing out because we had a “biweekly” status and was confusing people. We ultimately landed on not using the term.
Bimonthly and biannually have the same problem.
Yes, because I am a simpleton and Fortnightly and ‘twice a week’ already exists.
There are not two definitions. The prefix (bi) modifies the root (week). The suffix (ly) modifies the combination (biweek). Biweekly will always mean “once every two weeks” due to the order in which English dictates that the modifiers operate.
There are two definitions. The world of English disagrees with you.
There are two definitions, according to the major dictionaries I can view (OED requires a subscription):
https://www.merriam-webster.com/dictionary/biweekly https://dictionary.cambridge.org/dictionary/english/biweekly https://en.wiktionary.org/wiki/biweekly https://www.dictionary.com/browse/biweekly
So, the usage of biweekly as a synonym for semi-weekly is sufficiently high enough to land it in the dictionary, alongside a definition of every-two-weeks, and make biweekly an ambiguous and confusing term.
