Semiannual vs. Sesquiannual

Semiannualadjective

Biannual: occurring twice a year

Sesquiannualadjective

Occurring once every one and a half years (i.e. once every 18 months).

Semiannualnoun

Something occurring twice each year.

Semiannualadjective

Half-yearly.

Semiannualadjective

occurring or payable twice each year