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biannual vs. semiannual

biannual vs. semiannual: What's the difference?

Biannual and semiannual can both mean “twice a year.” However, biannual can also mean “every two years,” and semiannual can also mean “lasting for half a year” (though this sense isn’t commonly used). The best way to be clear is to just say “twice a year” or “every two years.”

biannual

[ bahy-an-yoo-uhl ]
adjective
  1. occurring twice a year; semiannual.
  2. occurring every two years; biennial.

semiannual

[ sem-ee-an-yoo-uhl, sem-ahy- ]
adjective
  1. occurring, done, or published every half year or twice a year; biannual.
  2. lasting for half a year: a semiannual plant.