bi-

or bin-

prefix

1. a. Two: biform.
   b. Both: binaural.
   c. Both sides, parts, or directions: biconcave.
2. a. Occurring at intervals of two: bicentennial.
   b. Usage Problem Occurring twice during: biweekly.
3. 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.

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.