I can confirm that the proper OED has the same definition. "Bi- 2a occurring twice in every one or once in every two (biweekly)" Biannual is only defined as o

I can confirm that the proper OED has the same definition. "Bi- 2a occurring twice in every one or once in every two (biweekly)" Biannual is only defined as occurring twice a year though. So, inflammable.