bin-

1. 1. Two: biform.

   2. Both: binaural.

   3. Both sides, parts, or directions: biconcave.

   4. Occurring at intervals of two: bicentennial.

   5. Usage Problem Occurring twice during: biweekly.

   6. Containing twice the proportion of a specified chemical element or group necessary for stability: bicarbonate.

   7. Containing two chemical atoms, radicals, or groups: biphenyl.

2. 1. Occurring at intervals of two: bicentennial.

   2. Usage Problem Occurring twice during: biweekly.

   3. Containing twice the proportion of a specified chemical element or group necessary for stability: bicarbonate.

   4. Containing two chemical atoms, radicals, or groups: biphenyl.

3. 1. Containing twice the proportion of a specified chemical element or group necessary for stability: bicarbonate.

   2. 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.