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According to Webster online, both semi-annual and bi-annual mean the same thing, i.e., twice a year. It may have different usage outside the states. The correct term for once every two years is biennial and every four years is quadrennial.
According to Webster online, both semi-annual and bi-annual mean the same thing, i.e., twice a year. It may have different usage outside the states. The correct term for once every two years is biennial and every four years is quadrennial.