Biannual, biennial, semiannual, though not synonymous, are frequently confused.
The chief source of confusion is biannual, which is used to mean either twice a year or every two years. If no clue to its meaning is given by the text, the reader will often be at a loss to determine the time represented.
- You will need to have a routine biannual examination.
Because of this ambiguity there is a tendency to avoid biannual and use the other two terms to express the two meanings.
Biennial unequivocally means existing for two years or happening every two years.
- The workers were strongly against the biennial election.
Semiannual is also unequivocal, since it means half-yearly, that is, twice a year.
- For detailed information, investors shall read carefully the semi-annual reports.