Bi-annual refers to an event or occurrence that happens twice a year, such as bi-annual budget planning or bi-annual dental checkups. However, there are several synonyms for this word that can be used interchangeably, including semiannual, biennial, and twice-yearly. Semiannual is the most commonly used synonym and refers to anything happening twice a year, while biennial refers to something happening once every two years. Twice-yearly is more informal but conveys the same meaning as bi-annual. Using these synonyms in your writing can add variety and precision to your language, making your message clear and concise.