bi-, bin-, bino-, bis-

(Latin: two, twice, double, twofold; a number; it normally functions as a prefix)

This bi- is used before s, c, or a vowel. Don't confuse this bi- with another one which means "life".

All words except biennial referring to periods of time and prefixed by bi- 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".

biacid (adjective) (not comparable)
Capable of combining with an acid in two different proportions: Biacid salts are salts that have two hydrogen atoms that can be exchanged with negative atoms or radicals.
biangular (buy-ANG-you-luhr) (adjective) (usually not comparable)
Pertaining to something that has two divergent sides: The Grande Arche of France is considered to be a biangular structure because the building is shaped like an upside down V.
1. Happening twice each year; semiannual.
2. Occurring every two years; biennial.

A biannual event occurs twice a year; a biennial event takes place once in two years.

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 ["biannual"]), and for the other sense to use the phrase "every two" (every two months; every two weeks; every two years [or in this case, "biennial"]).

biannual, biennial, perennial
biannual (bigh AN yoo uhl) (adjective)
Occurring twice a year; semiannual: The family got together on a biannual basis to celebrate birthdays.
biennial (bigh EN ee uhl) (adjective)
Occurring every two years: Electing senators occurs on a biennial basis.
perennial (puh REN ee uhl) (adjective)
Persistent over a period of several years; continuing without interruption: The flowers in the border around the garden were of a perennial nature, ensuring bright colors year after year.

Edna's country cousins come to visit on a biannual basis; however, her cousins who live across the ocean come here on biennial trips. It is always great fun to garden together; Jane and Carmen like to plant perennial flowers which will be in bloom whenever their cousins come to visit them.

Dual sovereignty, government by two.
biarticulate (adjective) (not comparaable)
Pertaining to having, or consisting of, two joints: The antennae of certain insects is one example of biarticulate creatures.
biathlon (s) (noun), biathlons (pl)
1. A contest in which cross-country skiers, carrying rifles, shoot at targets at four stops along a 12.5-mi. (20 km) course.
2. An athletic contest comprising of any two consecutive events.
biaxial (adjective) (not comparable)
Referring to something that possess two axes: Some crystals are biaxial in that they have two optical axes in which a birefringence does not take place.

A bicameral government has two legislative branches or chambers, like the House and the Senate of the United States.

The composite curve of an electrocardiogram representing the combined effects of the right and left ventricles.
bicentennial (adjective) (not comparable)
1. Relating to the 200th anniversary of an event or happening.
2. Something that happens every two hundred (200) years.
bicentric (adjective)