Definition of bi- in English:


combining form

  • 1Two; having two:

    See also bin-
    1. 1.1 Occurring twice in every one or once in every two:
    2. 1.2 Lasting for two:
    3. 1.3 Doubly; 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.