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• bi
  bi

  adjective

  bisexual.
• Bi
  Bi

  bismuth.
• BI
  BI

  abbreviation

  built-in.
• bi-
  bi-

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

bi

¹ American  

[bahy] / baɪ /

adjective

bis, plural bi's plural

1. Slang. bisexual.

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Bi ² American  

Symbol, Chemistry.

1. bismuth.

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BI ³ American  

abbreviation

BI's plural

1. built-in.

2. business intelligence.

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bi- ⁴ American  

1. a combining form meaning “twice,” “two,” used in the formation of compound words.

   bifacial; bifarious.

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bi- ⁵ American  

1. variant of bio-, especially before a vowel.

   biopsy.

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bi- ¹ British  

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. 1. denoting an organic compound containing two identical cyclic hydrocarbon systems

      biphenyl

   2. (rare in technical usage) indicating an acid salt of a dibasic acid

      sodium bicarbonate

   3. (not in technical usage) equivalent of di- 1

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Bi ² British  

symbol

1. bismuth

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bi ³ British  

/ baɪ /

adjective

1. slang short for bisexual bisexual

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bi- ⁴ British  

combining form

1. a variant of bio-

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bi ⁵ British  

abbreviation

1. Burundi

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Usage

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.

Commonly Confused

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 ).

Etymology

Origin of bi¹

By shortening

Origin of bi-⁴

< Latin, combining form of bis; see twice

Example Sentences

Given the reduced need for a hawkish response, BI is likely to rely on non-rate tools for rupiah stability, ING’s Deepali Bhargava says.

From The Wall Street Journal • Apr. 23, 2026

Expectations for a near-term resumption of easing have been scaled back, with BI likely to remain in a wait-and-see mode, he added.

From The Wall Street Journal • Mar. 17, 2026

ANZ Research economists think there is scope for BI to lower rates on the back of the Fed move and as global risk sentiment continues to hold up.

From The Wall Street Journal • Dec. 12, 2025

Other retailers are testing ways to prevent shoplifting, BI reported.

From Salon • Jan. 15, 2025

For example, the "Make Money Fast" pyramid scheme exceeded a BI of 20 a long time ago, and is now considered "cancel on sight".

From The Jargon File, Version 4.2.2, 20 Aug 2000 by Steele, Guy L.