[ bahy ]
/ baɪ /
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adjective, noun, plural bis, bi's.
Slang. bisexual.
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Origin of bi

By shortening

Other definitions for bi (2 of 5)


Symbol, Chemistry.

Other definitions for bi (3 of 5)



Other definitions for bi (4 of 5)


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

Origin of bi-

<Latin, combining form of bis;see twice

words often confused with bi-

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 ).

Other definitions for bi (5 of 5)


variant of bio-, especially before a vowel: biopsy.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does bi- mean?

Bi- is a combining form used like a prefix, and it means “two” or “twice.” It is often used in scientific terms, but it crops up in everyday language as well.

Bi- comes from Latin bis, meaning “twice, doubly.” The Greek equivalent of this combining form is di-, as in diacid.

What are variants of bi-?

Bi- is related to the combining form bin and is used with some words or word elements beginning with vowels. These two forms have similar origins, and for that reason, the difference between the two is a small yet important nuance: bi- often means “twice,” while bin- typically means “double.”

Want to know more? Read our Words That Use bin- article.

Examples of bi-

An example of a word you may have encountered that features bi- is biannual, which can mean either “occurring twice a year” or “occurring every two years.”

Confused? You’re not alone! When it comes to indicating dates on the calendar, bi- likes to have it both ways, as it were. Learn some tips on using biannual and other tricky terms like biweekly here.

We know bi- means “twice,” but what about the -annual portion of the word? You guessed it: -annual means “yearly,” from Latin annuālis. Biannual literally translates to “twice yearly.”

What are some words that use the combining form bi-?

The following words use the equivalent forms of bi- in Latin:

What are some other forms that bi- may be commonly confused with?

There are many words that begin with the letters bi-, such as bias, that do not use the combining form bi- to denote “two.” Learn what words like bias and bilk mean at our entries for these words.

Break it down!

Humans, like many animals, are considered bipeds. The combining form -ped means “(having a) foot.” With this in mind, what is the literal meaning of biped?

How to use bi in a sentence

British Dictionary definitions for bi (1 of 5)

/ (baɪ) /

adjective, noun

British Dictionary definitions for bi (2 of 5)


the internet domain name for

British Dictionary definitions for bi (3 of 5)


the chemical symbol for

British Dictionary definitions for bi (4 of 5)


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

British Dictionary definitions for bi (5 of 5)


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

Scientific definitions for bi


The symbol for bismuth.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.