Meaning of BI- in English
a combining form meaning "twice," "two," used in the formation of compound words: bifacial; bifarious. Cf. bin- .
[ bis; see TWICE ]
Usage . 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 ).
var. of bio- , esp. before a vowel: biopsy.
Random House Webster's Unabridged English dictionary. Полный английский словарь Вебстер - Random House . 2012