Definition of bi- in English:

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Pronunciation: /bī/
(often bin- before a vowel)


1Two; having two: bicolored biathlon binocular
1.1Occurring twice in every one: biannual bimonthly
1.2Occurring once in every two: bicentennial biennial
1.3Lasting for two: biennial biennium
1.4Doubly; in two ways: biconcave
1.5 Chemistry A substance having a double proportion of the radical, group, etc., indicated by the simple word: bicarbonate binoxalate
1.6 Botany & Zoology (Of division and subdivision) twice over: bipinnate


The meaning of bimonthly (and other similar words such as biweekly and biyearly) is ambiguous. Bimonthly, for instance, can mean either ‘occurring or produced twice a month’ or ‘occurring or produced every two months.’ So, if an organization holds bimonthly meetings, over the course of a year, will it meet six times or twenty-four times? The only way to avoid this ambiguity is to use alternative expressions like every two months and twice a month. See also biennial (usage).


From Latin, earlier dui-, related to Greek di- 'two' and Sanskrit dvi- 'doubly, having two'.

For editors and proofreaders

Syllabification: bi-

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