Ask 5 well-educated native English speakers, and I wouldn’t be surprised if you get 5 different answers:
What’s the difference between bi-annual and semi-annual?
If you guessed:
semi-annual = twice per year bi-annual = every other year
you would be WRONG!
Bi-annual and semi-annual mean the same thing: twice per year.
Biennial means every other year.
Don’t believe me? Look it up. Wait: that won’t work. Literally half the online resources I consulted had the definitions wrong, and many had irate reader corrections.
FYI: Merriam-Webster, Oxford, and American Heritage got it right. Now, if they could just agree if its bi-annual and semi-annual or biannual and semiannual.