Biweekly is not its own antonym but it means two completely different things (every other week and twice a week) which for me as rendered it useless since you c

Biweekly is not its own antonym but it means two completely different things (every other week and twice a week) which for me as rendered it useless since you cannot know which meaning is intended. The best way to deal with this issue is to have body that slows down language changes, then normalise them based on logic and history, something like the https://en.m.wikipedia.org/wiki/Royal_Spanish_Academy https://en.m.wikipedia.org/wiki/Royal_Spanish_Academy.