BTW, I know that "semi" has an original Latin meaning of "half" but it has lost precision in English e.g. semi permanent != half permanent.

Please do not use "semi [period]" to mean "twice per [period]" or "once per half [period]". For comments here, it seems to have traction in the US but it certainly does not have traction outside the US. "Semi" means "partially", with implications of 100% > semi > 50% (e.g. something that is more soft than hard is semi-soft. It's more than half soft - or it'd be semi-hard - but less than 100% soft). In terms of time, semi can mean something like "not quite a [period]" e.g. semi monthly = not quite monthly. Given that this is frequency, not quite monthly does not mean "more often than once a month" it means "not as often as a month". So semi still means less often than monthly, but without a known or exact cadence. Long story short, semi is nowhere near accurate enough to mean "twice" or "half" or anything to do with a specific number.