Once per semi-annuus or semi once-per-annuus? Halfyear-ly or half-yearly?
Just get off the Latin high horse and say twice yearly or once every two years to avoid any misunderstanding. π€£
"biennial" is supposedly unambiguous for once every two years but your readers won't all know that anyway.
infosec.exchange/@adamhotep/11β¦ , thanks @Adam Katz :donor: