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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

With “Resurrection,” Bi delivers something uncommonly rich, boldly conceiving his latest as a salute to the history of film.

From Los Angeles Times • Dec. 12, 2025

This wistful chapter evokes classics like “Paper Moon,” but Bi lands on a resolution that’s uniquely heartbreaking, connecting the illusion of movies with the delusions we cling to in the real world.

From Los Angeles Times • Dec. 12, 2025

One of the men, Theodore Bi, called the work “an idea anyone can get behind” and said they had intended to give it as a gift to Elon Musk.

From New York Times • Nov. 20, 2024

The Pantastic Bi-Mo Bi-Bar Pride 2024: Join the Seattle Pan Bi Alliance this Pride month for this bimonthly Pantastic Bi-Mo Bi-Bar to meet up with other bi/pan+ folks for drinks and conversation.

From Seattle Times • May 31, 2024

She watched one of Diko’s yellow eyes flick in her direction before he suddenly lunged, jaws snapping at Bi Mutunga’s sandaled feet.

From "Beasts of Prey" by Ayana Gray