b. Usage Problem Occurring twice during: biweekly.
a. Containing twice the proportion of a specified chemical element or group necessary for stability: bicarbonate.
b. Containing two chemical atoms, radicals, or groups: biphenyl.
[Latin bis, bi-, twice, and bn, two by two; see dwo- in Indo-European roots.]
Usage Note: Bimonthly and biweekly mean once every two months and once every two weeks. For twice a month and twice a week, the words semimonthly and semiweekly should be used. Since there is a great deal of confusion over the distinction, a writer is well advised to substitute expressions like every two months or twice a month where possible. However, each noun form has only one sense in the publishing world. Thus, a bimonthly is published every two months, and a biweekly every two weeks.