a combining form meaning “twice,” “two,” used in the formation of compound words: bifacial; bifarious.
Compare bin-.

< Latin, combining form of bis; see twice

All words except biennial referring to periods of time and prefixed by bi-1 are potentially ambiguous. Since bi- can be taken to mean either “twice each” or “every two,” a word like biweekly can be understood as “twice each week” or “every two weeks.” To avoid confusion, it is better to use the prefix semi- to mean “twice each” (semiannual; semimonthly; semiweekly) or the phrase twice a or twice each (twice a month; twice a week; twice each year), and for the other sense to use the phrase every two (every two months; every two weeks; every two years). Unabridged


variant of bio-, especially before a vowel: biopsy. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
bi- or (sometimes before a vowel) bin-1
combining form
1.  two; having two: bifocal
2.  occurring every two; lasting for two: biennial
3.  on both sides, surfaces, directions, etc: bilateral
4.  occurring twice during: biweekly
5.  a.  denoting an organic compound containing two identical cyclic hydrocarbon systems: biphenyl
 b.  (rare in technical usage) indicating an acid salt of a dibasic acid: sodium bicarbonate
 c.  (not in technical usage) equivalent of di-
[from Latin, from bistwice]
bin- or (sometimes before a vowel) bin-1
combining form
[from Latin, from bistwice]

combining form
a variant of bio-

bio- or (before a vowel) bi-
combining form
1.  indicating or involving life or living organisms: biogenesis; biolysis
2.  indicating a human life or career: biography; biopic
[from Greek bios life]
bi- or (before a vowel) bi-
combining form
[from Greek bios life]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

prefix meaning "two, twice, double," etc., from L. bi-, from Old L. dvi- (cognate of Skt. dvi-, Gk. di-, O.E. twi-), from PIE base *dwo- "two." Nativized from 16c.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

bi- 1 or bin-

  1. Two: bilateral.

  2. Both: binaural.

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

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

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

bi- 2
Variant of bio-.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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