Definition of bi- in English:


  • 1Two; having two.

    See also bin-
    1. 1.1Occurring twice in every one or once in every two.
    2. 1.2Lasting for two.
    3. 1.3Doubly; in two ways.
    4. 1.4Chemistry (in names of compounds) containing two atoms or groups of a specified kind.
    5. 1.5Chemistry Denoting an acid salt.
    6. 1.6Botany Zoology (of division and subdivision) twice over.


The meaning of bimonthly (and other similar words such as biweekly and biyearly) is ambiguous. Such words can either mean ‘occurring or produced twice a month’ or ‘occurring or produced every two months’. The only way to avoid this ambiguity is to use alternative expressions like every two months and twice a month. Biannual and biennial are also confusing: biannual means ‘occurring twice a year’ and biennial means ‘occurring every two years’


From Latin, ‘doubly, having two’; related to Greek di- ‘two’.