Technically, a biweekly meeting occurs every two weeks and a semiweekly one occurs twice a week; but so few people get this straight that your club is liable to disintegrate unless you avoid these words in the newsletter and stick with “every other week” or “twice weekly.” The same is true of “bimonthly” and “semimonthly,” though “biennial” and “semi-annual” are less often confused with each other.