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".