Canadian here, with 50 years in the workforce. I’ve never once been paid semi-weekly or bimonthly. Here, biweekly is every two weeks semi-monthly is every half month. Obviously, that latter is often spoken of as twice a month, which just adds to the confusion between “bi” and “semi”.

The reality is that these words, like most words (at least in English), mean whatever the speaker wants them to mean and consensus can be hard to reach.

I give you the phrase “table the discussion”. Sometimes it means to formally bring something up for discussion. Other times it means setting the discussion aside for future consideration.

Or, my favourite from my childhood, “fat chance” which means that something is even less likely than if it had a slim chance. Granted, that might be more in the line of idiomatic slang, but it stands as part of at least the era’s Canadian English that did have broad consensus and still does, I think.

That seems backwards to me. Mainly because if you move it to years instead of weeks, something that happens twice a year happens in half a year (semiannual) while something that happens every other year happens in 2 years (biannual).

Of course, I guess you you argue that it isn’t much time for the thing to happen, but how many times it does happen. The shareholders meeting happens in January and July, so it happens twice in a year, and it should be semiannual. This is because it happens is semi-year, or 6 months. But you could argue that it happens twice in a year, so has bi-annually.

I realized I may have talked out of my original point, but I feel like my initial comment (semiannual is 6 months, and biannual is 24 months) is easier to understand.