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

Nearby words

  1. bhutto,
  2. bhutto, benazir,
  3. bhutto, zulfikar ali,
  4. bi,
  5. bi sex,
  6. bi-bi reaction,
  7. bi-bivalent,
  8. bi-curious,
  9. bi-level,
  10. bi-swing

Compare bin-.

Origin of bi-

< Latin, combining form of bis; see twice

Usage note

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 ).



variant of bio-, especially before a vowel: biopsy. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for bi-



sometimes before a vowel bin-

combining form

two; having twobifocal
occurring every two; lasting for twobiennial
on both sides, surfaces, directions, etcbilateral
occurring twice duringbiweekly
  1. denoting an organic compound containing two identical cyclic hydrocarbon systemsbiphenyl
  2. (rare in technical usage) indicating an acid salt of a dibasic acidsodium bicarbonate
  3. (not in technical usage) equivalent of di- 1 (def. 2a)

Word Origin for bi-

from Latin, from bis twice

combining form

a variant of bio-
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for bi-


word-forming element meaning "two, twice, double, doubly, once every two," etc., from Latin bi- "twice, double," from Old Latin dvi- (cognate with Sanskrit dvi-, Greek di-, Old English twi- "twice, double"), from PIE root *dwo- "two." Nativized from 16c. Occasionally bin- before vowels; this form originated in French, not Latin, and might be partly based on or influenced by Latin bini "twofold" (see binary).

Online Etymology Dictionary, © 2010 Douglas Harper